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Fig. 636. Diagrammic Circuit of Completed Connection in 10,000 Line Automatic System (See Page 524). 




















































































































































































































































































































































































































































TELEPHONOLOGY. 


A DESCRIPTION OF M00E0N TELEPHONE APPLIANCES. 


A Common Sense Treatise on the Erection, Equipment and 
Maintenance of Telephone Exchanges. 

Line. Instrument and Switchboard Troubles 

and Their Remedies. 


Apparatus. Line and Cable Testing. 


BY 


H. R. VAN DEVENTER, B. S., E. E. 

ASSOCIATE MEMBER AMERICAN INSTITUTE OF ELEC¬ 
TRICAL ENGINEERS. MEMBER OF THE FRANK¬ 
LIN INSTITUTE AND OF THE AMERICAN 
ELECTROCHEMICAL SOCIETY. 


SPECIAL ARTICLES BY EMINENT EXPERTS. 



SUMTER, S. C.. 
1 909 . 







Copyrighted 1907 

BY 

H. R. Van Deventer 

AND 

F. C. Manning. 



TYPESETTING AND PRESSWORK BY OSTEEN PUBLISHING CO., 
SUMTER, S. C, 


LIBRARY of CONGRESS 
Two Codes Received 

MAV 7 1$J09 

. . . Copvn,...: ,,- v 

l r - v J*- 

l z 3LH s 







CHARLES THOMAS MASON. 

OF SUMTER, SOUTH CAROLINA« 

WHOSE MANY INVENTIONS HAVE ADVANCED THE ART OF TELEPHONY, 


THIS WORK IS DEDICATED 










































ACKNOWLEDGMENT. 


The author desires to express his indebtedness to the manufacturing 
companies and technical publications for the assistance they have given 
him, and for cuts, circuit prints and other data, which has made this work 
possible. 

No originality is claimed for this book. The field of telephony is so 
wide, that it would be practically impossible for one author to prepare a 
general work of this nature in any reasonable time, and have it contain 
much original matter; therefore with a view to presenting a book contain¬ 
ing accurate, useful and up-to-date descriptions and data, and one that 
would not be out of date before it was published, the author has used many 
articles prepared by specialists, and also much matter from the technical 
press. 

Many of the diagrams and cuts of apparatus were made especially for 
this work, which represents an effort to present an easily understood 
treatise on the subject, free from technical terms and phrases, and suited 
for use by the great mass of practical workers in the telephone field. 

THE AUTHOR. 


March, 1909. 













































CONTENTS. 


CHAPTER I. 

FIRST PRINCIPLES, TALKING EQUIPMENT.1 

Sound — Vibration — Pitch — Intensity — Musical Sounds—Noise— 
Range of Vibrations in Telephone Transmission—Amplitude of 
Vibrating Bodies—How Sound Waves reach the Ear—Construc¬ 
tion of the Ear—Magnetism—Natural Magnets—Lines of Force 
—North and South Poles—Arrangement of Receiver—Trans¬ 
formation of Sound into Electrical Energy—Grounded Circuits 
—Metallic Circuits—Transmitters—Regulation of Battery Flow 
—Volt—Ohm—Ampere—Induction Coil—Theory of Operation 
of Complete Telephone. 


CHAPTER II. 


SIGNALLING EQUIPMENT, ..10 

Battery Bell—Telephone Ringer, Theory of Operation—Magneto 
Generator, Theory of Operation—Field—Current Waves— 
Cycles — Frequency — Alternations — Armature Construction 
Number of Magnet Bars—Hook Switches—Series Circuit—Self 
Induction—Unit of Self Induction—Bridging Circuit—Actual 
Construction of Ringer—Calculation of Winding of any Resist¬ 
ance for any Size Spool—Adjustment of Armature—Types of 
Commercial Ringers—Wire Gauge—Winding Machine—Testing 
Ringers—Calculating Resistance of Line with Series or Bridged 
Ringers—Ringer Troubles—Schwartz Ringer—Generator Con¬ 
struction—Size of Magnets—Construction of Armature—Gear 
Wheels—Shunt Springs—Testing Generators—Output of vari¬ 
ous Size Machines—Causes of Weak Magnets—A Magnet for 
Re-Magnetizing Generator and Ringer Magnets. 

CHAPTER III. 

COMMERCIAL TALKING EQUIPMENT.49 

Receiver—Diaphgram—Magnets—Spools—Different Types—Sumter 
—Western Elect. Co. (Bell)—Testing—Testing with Phonograph 
—Gauge for Pole Piece Adjustment—Methods of Winding 
Spools—Testing for Open Coil—Revolution Counter—Head Re¬ 
ceiver — Experimental Receivers — Transmitters — Carbon 

Diaphgram Type—Bell Transmitter—Size Granules—Distance 

vii 



viii 


CONTENTS 


Between Electrodes—Filling Chamber—Complete Bell Trans¬ 
mitter, Two Types—Kellogg Transmitter—Dean—Interstate— 
Double Diaphgram—Sumter—Current Consumption—Protecting 
Diaphgram—Induction Coils—Why Used—Assembly—Size of 
Core—Chucks for Holding Coils—Arrangement of Terminals— 
Testing Coils—Various Types of Coils—Locating Trouble. 

CHAPTER IV. 

MAGNETO INSTRUMENTS AND CIRCUITS,.T9 

Details of Complete Instruments—Styles of Cabinets—Old Series Cir¬ 
cuit—Later Series Arrangement—Standard Bridging Circuit— 
Special Bridging Circuit—Number of Phones on One Line— 
Condenser in Receiver Circuit—Direct Current Generator Cir¬ 
cuit—Central Relay for Grounded Lines—Calling Central Sepa¬ 
rately Over Grounded Lines—Calling Central Separately Over 
Metallic Lines—Telephone Wiring—Cable Wiring—Desk Stands 
Interchangeable Circuit Plates—Desk Stand Circuits—Location 
of Instrument Troubles—Lightning Arrester—Ground Wires— 
Ground Connections. 


CHAPTER V. 


MAGNETO SWITCHBOARDS,.102 

Switches for Two Lines—Key Switch—Plug Switch—Early Types of 
Drops—Armored Drops—Dean Drop—Monarch Drop—Western 
Elect. Drop—Sumter “Bulls Eye” Drop—Battery Restored 
Drops—Sumter “Unitype” Drop—Jacks—Plugs—Cords—Oper¬ 
ator’s Sets—Drop Circuits—Night Bell Circuit—Relay and Pilot 
Lamp Circuit—Diagram of Phones Connected—Operator Ring¬ 
ing—Operator Listening—Ringing and Listening Keys—Sub¬ 
scriber Ringing Off—Special Cord Circuits—Dean Cord Circuit 
With Condensers—Monarch Cord Circuit—Standard Cord Cir¬ 
cuit, Double Ringing Key—Cord Test Circuit—Recording Plugs 
—Generator Circuit—Pole Changer Circuit—Diagram of Pole 
Changer—Connecting Pole Changer to Switchboard—How to 
Make a Pole Changer—Operator’s Set, Circuit—Testing for 
Trouble in Switchboard Circuits—Reversed Lines—Reversed 
Cords—Locating Reversed Cords—Repeating Coils, various types 
—How to Make Repeating Coils—Repeating Coil in Cord 
Circuit—Talk Through and Ring Through Coils—Coil in Cord 
Circuit, with Cut Off Key—Looping up Cords—Testing Wires 
in Cables—Instructing Operators About Handling Cords—Tools 
for Switchboard Man—Small Switchboards—Ringer Indicators 
—Operation of Ringer Board—Circuits and Connections of Ring¬ 
er Board—Signal Ringing or “Relay” Drops—Dean Drop— 
Sumter Drop—Circuits for Relay Drops—Circuits of Small 
Board— 50 Line Board— 100 Line Board— 200 Line Board—Cabi¬ 
nets for Two Operators—Desk Type Cabinets—Kick Coil Sys¬ 
tems—Construction of Kick Coil—Transfer Systems—Order Cir¬ 
cuit—Multiple Trunking System—Theory of Multiple Trunking 
System—Theory of Multiple Switchboard—Series Multiple Sys¬ 
tem—Bridging Multiple System—Bell Self Restoring Drop— 
Busy Test. 


CONTENTS 


ix 


CHAPTER VI. 

SELECTIVE AND LOCK OUT SYSTEMS.175 

Two Party or “Duplex” System—Duplex Master Keys—Two Party 
System Using Schwartz Bell—Direct Current Generator—Four 
Party Biased Bell System—Biased Ringers—Four Party Master 
Keys—Biased Bells with Relay for Common Battery System— 
High and Low Frequency System—Zabel 8 Party System—Baird 
Secret Service System—Homer Roberts Selective and Lock Out 
System—Special Line Tests. 

CHAPTER VII. 


BATTERIES,.209 

Theory of Generation of Electricity by Chemical Action—Sal Ammon¬ 
iac Cell—Construction of Dry Cells—A Home Made Dry Cell— 
Fuller Cell—Gravity or Blue Stone Cell—Testing Batteries— 

Life of Batteries—Connecting Batteries—The Storage Battery— 
Positive and Negative Plates—Mounting and Connecting Cells— 
Mixing Electrolyte—Determining Polarity of Charging Current 
—Charging From D. C. Lighting Circuit—Observing Specific 
Gravity—Testing Electrolyte for Impurities—Color of Plates at 
Full Charge—Taking Battery Out of Service—Form for Keeping 
Charge Record—Form for Discharge Record—Yearly Test of 
Battery—How to Make a Storage Battery—Methods of Charg¬ 
ing—D. C. Charging Generator—Mercury Arc Rectifier—“Chem¬ 
ical” or Electrolytic Rectifier—How to Make a Chemical Rectifier 
—Measuring Internal Resistance of Batteries. 

CHAPTER VIII. 


TESTING TELEPHONE PARTS.237 

Transmitter Tests—Local Battery—Common Battery—Transmitter 
Resistance—Manufacture of Granules—Testing Transmission— 
Receiver Tests—Repeating Coil Tests—Generator Tests—Ringer 
Tests—Measuring Inductance. 

CHAPTER IX. 

TESTING EQUIPMENT AND FAULT LOCATION.265 

Portable Testing Sets—Wheatstone’s Bridge—Post Office Bridge—De¬ 
cade Bridge—Dial Decade Bridge—Slide Wire Bridge—Dimen¬ 
sions Fault Finder—Cable Testing Sets—Fisher Set—Galvano¬ 
meters—Insulation Measurements—Capacity Measurements— 
Location of Faults—Murray Loop—Loop With Post Office Bridge 
—Varley Loop With Post Office Bridge—Loop With Different 
Sized Conductors—Grounded and Crossed Wires—Continuity— 
Crosses—Two Faults on one Wire—Grounds—Correction for 
Lead Wires—Check Tests—Locating Opens—Leeds & Northrup 
Fault Finder for Resistance Measurements—Locating Fault, 




CONTENTS 

one bad and one good Wire, both same Size—Locating Fault, two 
Wires, Different Size—Check Test—Fault Location, Length of 
Faulty Wire Known—Opens in Telephone Cable—Open in Tele¬ 
graph Cable. 


CHAPTER X. 

MEASURING INSTRUMENTS AND THEIR USES,. 310 

Construction of Voltmeter and Ammeter—Theory of Operation— 
Pignolet Type—Resistance Measurements—Standard Voltmeter 
—Checking Voltmeters—Weston Meters—American—Whitney 
—Measuring Low Resistance—Resistance of Buss Bars—Resist¬ 
ance of Generator Armature—Resistance of Contacts in Knife 
Switches—Milli Voltmeters and Ammeters—Testing Condensers 
With Voltmeters—Line Tests—Testing Resistance of Coils With 
Voltmeter and Ammeter—Internal Resistance of Batteries With 
Volt and Ammeter—How to Make a Voltmeter or Ammeter— 

How to Make Slide Wire Bridges for the Location of Faults, and 
General Measurements. 


CHAPTER XI. 

COMMON BATTERY EQUIPMENT,.344 

Difference Between Magneto and Common Battery System—Common 
Battery Signals—Visuals—Lamp Signals—Ringing Circuits— 
Sources of Current Supply—Telephone Circuits—Transmitter 
and Receiver in Series—Receiver in Local Circuit of Induction 
Coil—Bell Coil and Circuits Used With It—Theory of Operation 
of Bell Coil—Retardation Coil Circuit—Balanced Bridge Coil Cir¬ 
cuit—Direct Current Receiver Circuit—Wall and Desk Sets— 
Circuits of Desk Sets—Lock Out Relays—Bell Common Battery 
Switchboard, Line Circuit—Cord Circuit—Pilot Circuit, Opera¬ 
tors Circuit—Busy Test Explained—Stromberg Carlson System 
—Line Circuit—Line Relays—Operator’s Circuit—Generator 
Circuit—Trunk Circuit—Busy Tests—Construction of Switch¬ 
board at St. Louis, Mo.—North Elect. Co’s. Circuit—Kellog Cir¬ 
cuit—Kellog Trunk—Vote-Berger Circuit, Ballast Switchboard 
—Circuits Using one Relay per Line—Bell Circuit Using Double 
Wound Line Relay—Connections in Main and Intermediate 
Frames—Troubles in Line Circuit—Open Sleeve—Cord Circuit 
—Repeating Coil—Connections of Various Coils—Common Bat¬ 
tery Cord Circuits—Cord Troubles—Resistance Coils—Lamps— 
Operators’ Circuit—Operators’ Induction Coils—Ringing and 
Listening . Key—Trunk Circuit—Operation of Trunk Circuit— 
Trunk Operator’s Set—Trunk Circuit With Automatic Ringing 
Keys—Operation of Auto. Trunk—Long Distance Toll Trunk—- 
Operation of Toll Trunk—Relays Used in Trunks—Testing 
Ringing Relays in Trunk Circuits—Trunk Test Sets—Tone Test 
Circuit—Plugging Up Lines—Howler Circuits—The Calcula- 
graph—Method of Mounting—Making Calculagraph Records. 



CONTENTS 


xi 


CHAPTER XII. 

HARMONIC PARTY LINE SYSTEMS.423 

Explanation of Principle of Operation—Early Systems—Discussion 
of Desirable Features Necessary in Successful Party Line Sys¬ 
tems—Design of Harmonic Ringer—Armature—Gong Adjust¬ 
ment—Dean Electric Co. Ringer and Harmonic Converter—Cir¬ 
cuits of Harmonic Converter—Power Consumption of Converter 
—Answers to Questions Regarding Converter—General Trouble 
Test—Adjusting Vibrator Contact Screws—Frequency Testing 
and Adjusting—Voltage Testing Apparatus—Care of Platinum 
Contacts—Replacing Platinum Contacts—Battery Reversing 
Circuits—Care of Dry Cells—Code Signal Ringing Connections 
—When Master Keys Are Used—When Individual Keys Are 
Used—Talking Battery Noise Killer—Frequency Meter—Meth¬ 
od of Operation—Stromberg Harmonic Ringer—Wiring of Har¬ 
monic Telephones— Haltzer-Cabot Converter—Master Key Cir¬ 
cuits. 


CHAPTER XIII. 

LINE AND CABLE CONSTRUCTION,.467 

Size of Poles—Staking—Distances—Railroad Crossing—Framing— 
Brackets—Cross Arms—Guying—Anchors—Distributing Poles 
—Tieing—Bracing—Making Guys—Stringing Wires—Table of 
Guy Wires—Reels—Drawing Up—Passing Through Trees— 
Tree Ladder—Length of Span—Tieing and Splicing—Table of 
Pounds Per Mile, etc., Line Wires—Noisy Lines—Transposi¬ 
tions—Home Made Iron Brackets—Connecting to Lightning Ar¬ 
resters Putting Up Telepone—Inside Wiring—Cable Boxes—Con¬ 
nections to Cable Boxes—Opening and Testing Cables to Switch¬ 
board—Connecting Grounded and Metallic Lines—Lightning 
Arresters and Distributing Frames—Heat Coils—Resetting Coils 
—Test Plugs—Intermediate Frames—Switchboard Cabling— 
Color Code—Running Jumper Wires—Aerial Cables—Specifica¬ 
tions for Lead Covered Cables—Talking Value of Different Size 
Cables—Different Methods of Measuring Capacity—Drawing 
Cable—Making Joints—Removing Moisture—Scoring the Lead 
—Removing Lead—Lead Sleeve—Weight of Sleeves—Joints on 
Paper Cables—Testing at Joints—Self-Soldering Nozzles—Pro¬ 
viding for Extensions—Combination Terminal Head and Junc¬ 
tion Box—Multiple Cable Distribution Cable Joints With Self- 
Soldering Nozzles—Locating Pairs in Cable—Cable Testing 
Sets. 

CHAPTER XIV. 


THE AUTOMATIC SYSTEM..517 

Early Development of Automatic System—Theory of Operation of 
Automatic System—Two and Three Figure Systems—Four and 
Five Figure System—Trunking System—Groups of Units—Send- 



Xll 


CONTENTS 


ing Mechanism and Its Operation—Circuit of Automatic Com¬ 
mon Battery Instruments—Operation of Switches—Connectors 
Switch—Circuits and Mechanism of Connector Switch—Busy 
Tests—Busy Release—Circuits and Mechanism of Selector 
Switch—Circuits of Line and Master Switch—Guide Shaft and 
Line Unit—Floor Plan of Exchange—Columbus, Ohio, Switch 
Room—Unit Exchanges. 









TELEPHONOLOGY. 


CHAPTER I. 


FIRST PRINCIPLES—TALKING EQUIPMENT. 


It is not the purpose of this book to give a complete history of the tele¬ 
phone from its first inception, but rather to deal with the different types 
of equipment together with the methods of installing and caring for same 
which are now on the market and in general use. For this reason no 
allusion will be made to the early inventions or types of equipment which 
preceded those now in use. 

To have a proper understanding of the operation of telephone appara¬ 
tus it is necessary to be somewhat familiar with the principles of sound. 
It is known that all sounds are caused by vibration. For instance; if a 
bell is struck, energy is imparted to its body, which is immediately set 
in motion, and this motion is termed “vibration”. The vibrations are 
transmitted to t,he air, which conducts them to the ear, where they strike 
upon several thousand little nerves located within the ear, producing in 
the mind the sensation of sound. 

A simple illustration of this is seen when a pebble is thrown into a 
a pond of water. Numerous small ripples occur at the point where the 
pebble strikes the water; these become larger and larger as they go fur¬ 
ther away from the centre point, and finally strike against the edge of the 
pond. 



Fig. 2. 


Fig. 1. 


It is exactly in this manner that a bell, or diaphragm of a receiver 
gives forth sound, which is carried through the air to the ear just as the 
ripples reach the land. Of course sound waves passing through the air 
are not visible to the sight as ripples of water are, but sound waves 
can be seen by the use of the necessary equipment, which is very simple, 
consisting of a tuning fork or other body, with a small needle or pointer 
attached. If the fork be thrown into motion and then drawn across a 
sheet of smoked glass, the vibrations of the needle on the end of the fork 
will scratch a light line or wave through the smoke on the glass. This 
is shown in Fig. 1. 

Sound possesses several characteristics. The principal ones with 
which we have to deal are pitch and loudness, or, as they are better 
















2 


TELEPHONOLOGY 


termed, intensity and quality. As all sound depends upon vibrations, the 
rate, or number of vibrations per second at which a body moves deter¬ 
mines the pitch of the sound. A noise is usually a set of vibrations hav¬ 
ing no definite time. This confused set of sound waves strikes the ear 
and produces an unpleasant sensation commonly known as noise. In other 
words, the different vibrations tend to confuse each other. 

A musical sound is almost the reverse of this, as it is a succession 
of clear, distinct vibrations so close together that they become blended 
into a harmonious whole. The difference between a noise and a musical 
sound will be seen by referring to Fig. 2, which shows a toothed wheel 
with a spring held against the teeth. If the wheel is slowly turned a 
succession of distinct clicks is heard which may be termed a noise, but 
if the speed of the wheel is increased so that sixteen teeth per second hit 
the spring then it is very difficult for the ear to distinguish the different 
strokes from each other, and a humming noise is the result. If the speed 
is increased an almost musical sound will be produced. 



Fig. 4. 


Fig. 3. 


Whether the sound produced is musical or not depends largely upon 
the material used, but the illustrations here given will serve to demon¬ 
strate the meaning of the term Pitch as applied to sound. 

Another common illustration is found in any musical string. When 
tightened to a certain degree and struck, a note is produced depending 
upon the number of vibrations or movements per second of the string. 
If the number of vibrations is sixty-four, the note is called “C” and is the 
lower “C” of the piano scale. 

If the string is stretched so that it vibrates more rapidly then the 
- pitch will be increased. For instance: if the vibrations number two hun¬ 
dred and fifty-six per second, we have middle “C”, and so on. 

From the foregoing it will be seen that the pitch depends upon the 
number, or, as it is termed, the frequency of vibrations per second. The 
human ear has the faculty of distinguishing musical sounds ranging from 
sixteen to thirty six thousand vibrations per second. The range of vibra¬ 
tions to be considered in telephonic transmission is between sixty and two 
thousand, which is well within the range mentioned. 

The velocity, or rate of speed, with which sound travels through the air 
is about one thousand one hundred feet per second. The rapidity with 
which sound travels depends to a great extent upon the temperature. 
This however has nothing to do with the transmission of telephonic 
sounds. 

A great deal of misunderstanding exists as to the operation of the 
telephone in transmitting sound, and it should be remembered that the 
sound waves are not transferred along the wire in the shape of sound 
vibrations, but are changed into electrical waves by the action of the in¬ 
strument, as described later. 

Loudness, or intensity of sound depends upon the distance through 
which the body causing the sound moves or vibrates. This distance is 
termed amplitude, and is illustrated by Fig. 3, in which an ordinary pair 






FIRST PRINCIPLES—TALKING EQUIPMENT 


3 


of telephone bells are shown; these are supposed to be ringing, and the 
dotted lines show that the bodies of the bells are vibrating or moving to 
a certain extent. If the clapper is made to vibrate harder, not faster, 
the bells will move through a greater distance, and the sound will be cor¬ 
respondingly louder. In other words, the harder a body is struck the 
greater the volume of sound will be produced, up to the limit of the body 
to produce sound. 

The quality of the note, or that which enables a distinction to be 
made between the sound given forth by different substances, such as a 
piece of wood, the head of a drum or a stringed instrument, depends 
upon the properties of the bodies, the substance of which they are com¬ 
posed, etc. It is very difficult to explain just why “C” on the piano and 
“C” as emitted by the human throat differ, but as this has very little bear¬ 
ing on the effect that sound produces in the telephone, it will not be dis¬ 
cussed here. 

The method by which sound waves reach the ear is very simple when 
you take into consideration that the atmosphere is made up of very fine 
particles or molecules. We will suppose that the bell, Fig. 4, is rung. 
Immediately the particles of air nearest the body of the bell will be 
forced out from it. These will strike the next particles and so on until 
the ear is reached. Air being an elastic substance, as soon as the first 
particles strike the second particles the first particles swing back and 
are again set in motion by the bell, and so on. This action is called wave 
motion, and takes place in all directions from the sounding body. In the 
case of the bell, the sound waves completely surround all portions of the 
gongs, as shown in Fig. 4. 



The human ear is shown in Fig. 5. A passage extends inwardly, 
across which is stretched a membrane. Immediately back of this is a 
small canal containing a fluid and several thousand nerves called the 
“Rods of Corti” which connect with the brain. If a certain note on the 
piano is struck, it will cause one of these rods to vibrate, and this vibra¬ 
tion will be transmitted to the brain and the sensation of sound will be 
produced. If a chord, or combination of musical sounds is made, several 
rods corresponding to the different sounds will vibrate, and this produces 
a harmonious sound. A noise may cause a great many of the rods to 
vibrate and this produces a confused sound like that caused by striking a 
number of keys on the piano at once. 

Some people have more of these nerves of hearing than others, and 
upon the number of these nerves depends a person’s capacity for hearing 




4 


TELEPHONOLOGY 


a number of sounds. The majority of people have nerves corresponding 
to the range previously mentioned. 

As a rule, solid substances conduct sound better than air. An illus¬ 
tration of this is shown in the ordinary child’s telephone, which consists 
of a couple of tin cans with a piece of paper or bladder stretched across 
the ends, connected by a string. As long as the string is held tight, the 
vibrations are carried along it without spreading out in all directions, 
which would be the case if the string was not used. 

From the foregoing it will be seen that a body in a state of vibration 
gives forth sound, and it is upon this fact that the action of the telephone 
depends, so far as receiving sound and emitting it at the other end of the 
line is concerned. The sound waves emanating from the throat of the 
speaker strike upon the diaphragm of the transmitter. Here they are 
transformed into electrical currents by the action of the instrument, as 
will be explained later, and are transmitted along the wire in the form of 
electrical energy to the receiver at the other end of the line, where in turn 
they cause the diaphragm of the receiving instrument to vibrate. These 
vibrations in turn reach the ear, and convey the idea of speech to the mind. 
It will be noted that the sound waves are transformed from mechanical 
vibration into electrical' energy and then back to mechanical vibration 
again. 



Fig. 6. 

Before proceeding to consider the telephone proper it is necessary 
to review the theory of magnetism, upon which the operation of the tele¬ 
phone depends. 

A magnet (so called from the fact that iron ore from Magnesia in 
Asia Minor was early known to possess this property) is usually a piece 
of steel having the power of attracting iron. 

Natural magnets are an ore of iron generally known as loadstone 
(Saxon, leaden, to lead) but are seldom met with, and are never used in 
telephone work. 

Commercial magnets are made by subjecting steel bars, either 
straight or in U shaped form to the magnetizing influence of an electric 
.current. This is usually done by placing them inside a hollow coil, or a 
piece of steel can be magnetized by simply bringing it in contact with 
another magnet. 

The principal property of a magnet is the ability to attract iron and 
to retain this power of attraction for an indefinite period. 

The operation of the first telephone, or as it is now called the “Re¬ 
ceiver” depends upon the fact that if a piece of iron is brought near to a 
permanent magnet, the invisible magnetic lines of force which exist in 
the neighborhood of the magnet are varied, and if the piece of iron is 
moved, a corresponding movement of the lines of magnetic force takes 
place. 




FIRST PRINCIPLES—TALKING EQUIPMENT 5 

This will be understood by reference to Fig. 6, where a piece of steel 
in an unmagnetized state is shown at “A.” The small arrows represent 
the molecules or particles of which the steel is composed. 

When the steel is magnetized the particles range themselves in a defi¬ 
nite direction, as shown at “B.” This arrangement is not visible to the 
naked eye, nor can it be seen, but manifestations that this change has taken 
place are very evident from the fact that the steel will now attract other 
pieces of iron, which proves that the magnetic effect is not only present in 
the steel itself, but exists in the air near the magnet in all directions. It is 
much stronger at the ends of the bar than in the middle, the absolute cen¬ 
tre being neutral, and this is taken advantage of in making telephone receiv¬ 
ers and other electrical instruments by bending the bar into a “U” shaped 
form, so that the attractive power of both ends can be used. This radia¬ 
tion of magnetic lines of force is shown in Fig. 7, which also shows that 
the greater number of lines, or the greatest strength, is at the ends of the 
magnet. 

If a magnet is suspended so that it is free to turn, it always tends 
to point north or south. The end which turns to the north is called the 
north pole, while the other end is called the south pole. The flow of the 
lines of force is from the north pole to the south pole. 

If a small piece of iron be brought near a magnet, it will become 
magnetized, and immediately changes the position of some of the lines of 
force near the magnet. This is shown in Fig. 8. 



FIG. 7. FIG. 8. 


It will be noted that the lines of force concentrate towards the piece 
of iron. If the iron be moved near to the magnet or further away from 
it, a corresponding movement of the lines of force will take place. 

If the magnet is arranged as shown in Fig. 8, having in front of it a 
thin piece of soft iron called in telephone work a diaphragm, and sound 
waves strike upon the latter, it will vibrate, and this movement will cause 
a corresponding movement of the magnetic lines of force about the end 
of a magnet. This is what takes place when an ordinary telephone 
receiver is spoken into. 

Some means must now be devised to transform the magnetic vibra¬ 
tions caused by the movement of the magnetic lines, into electrical vibra¬ 
tions, and to transfer these electrical vibrations along the wire to the 
other end of the line. This is accomplished by winding a coil of wire 
upon the end of the permanent magnet, and varying the lines of magnetic 
force which surround the coil by reason of its nearness to the magnet. 

Fig. 9 shows two receivers with the wire coils in place upon the 
heads of the magnets. The coils are connected together by the lines 
“L”-“L”. If the diaphragm of the receiver “A" is vibrated, the magnetic 
lines about the end of the magnet are moved. This creates a current of 






















6 


TELEPHONOLOGY 


electricity in the coil of wire, which travels over the line and into the 
coil of the instrument “B”. Here the process is reversed, and the current 
in the coil influences the magnet, so that the lines of magnetic force are 
varied. This produces a coresponding movement of the diaphragm at 
“B”, which in turn gives forth a sound identically similar in every way 
to that spoken into instrument “A”. 



The first telephone line consisted of two receivers, as above described, 
connected together by means of one wire, the earth being used in place of 
the other wire. At this time there were no other wires carrying sufficient 
current, to cause disturbances, as will be described later, and therefore 
grounded circuits, as the above arrangement is termed proved very satis¬ 
factory. But, owing to the rapid increase in electric light and trolley 
service, grounded circuits are no longer of value, as the heavy currents 
from the power wires cause disturbances in the telephone circuit. Two 
wires, or as it is termed, metallic circuits should therefore always be 
used. 

Another reason for not using grounded circuits is that if the differ¬ 
ent lines run parallel to each other for any distance, “Cross-talk” will 
result. This does not occur when metallic lines are used as they can be 
transposed as described later to remedy the trouble. Grounded lines can 
not be transposed. 

Sometimes, while there are no electric currents traversing the earth 
at the exact point where a grounded telephone line is located, still, if this 
grounded line is connected to a line several miles long, the currents in 
the earth, or as they are termed, “earth currents”, will seriously interfere 
with the operation of the line. In view of the fact that nearly all tele¬ 
phone exchanges are now being equipped for long distance service, it is 
well to mention here that only metallic circuits should be used. 

Two receivers connected together serve very well for a telephone 
line for a distance of several miles, the speech although weak, being very 
clear. For business purposes such a line would be practically worthless. 
It was therefore necessary to devise some means of increasing the power 
of the instrument. This was accomplished by the invention of the trans¬ 
mitter, which acts as an electrical valve. When the diaphragm is vibrat¬ 
ed, the transmitter allows more or less of the electrical current to pass. 
This will bp undprstood by reference to Fig. 10, where the transmitter is 
shown at “A”. ITjlpe diaphragm “D” is connected to one side of the Re¬ 
ceiver “R”. $et\yeen the diaphragm and “E”, or the back “electrode”, 
as it is termed, is placed a quantity of fine carbon, commonly known as 
granular carbon, and resembling coal dust. The battery is connected to 
the other terminal of the receiver, while the other side of the battery is 
connected to Electrode E. 

We will now consider the battery as a tank of water, Fig. 11, and 
will consider the transmitter as a valve “V”, while the receiver will be 
represented by the wheel “W”, supposed to be placed in the pipe in such 










FIRST PRINCIPLES—TALKING EQUIPMENT 


7 


a manner that when the water is flowing through the pipe the wheel will 
turn. If the valve “V” be almost closed, very little water will flow, and 
the wheel will turn slowly; but if the valve be open, allowing considerable 
water to flow, then the wheel will turn faster. This is practically what 
happens when the transmitter is used in connection with the receiver. 
When the former is spoken into, the sound waves strike upon the 
diaphragm. This moves it nearer to or further away from the back 
electrode. When the pressure is increased, more current from the battery 
will flow. When the pressure is diminished, which happens when the 
diaphragm springs back again, after having been pushed inwardly by 
the sound waves, less current will flow. This movement back and forth 
of the transmitter diaphragm causes current to flow along the line, and the 
current passes over the line and through the coils of the receiver, operating 
same as previously described. This arrangement increases the ability of 
the telephone to transmit speech, and it was the invention of the trans¬ 
mitter that made the telephone a practical success. 



Fig. 10. 


Fig. 11. 


There yet remained several difficulties to overcome, One of these, 
and the greatest, was the fact that any wire opposes the passage of an 
electric current just as water is impeded in its progress through 
a pipe by friction. In the case of an electrical current this friction is 
termed “resistance”. 

While the pressure of water or steam in a boiler is measured in units 
of pounds to the square inch, the pressure of electrical currents is meas¬ 
ured in units termed “volts.’ 

While a quantity of water is measured in quarts or gallons, a quan¬ 
tity of electricity is measured in units called “amperes.” 

The resistance a body offers against being moved is termed friction, 
and the electrical unit of friction, or resistance, is termed on “ohm”. 

A VOLT is that pressure of electricity necessary to drive one ampere 
of current through a resistance of one ohm. 

An OHM is that resistance which requires one volt to send a current 
of one ampere through it. 

An AMPERE is the amount of current that will pass through one 
ohm at a pressure of one volt. 

A simple manner of expressing Ohm’s law, that will be easily under¬ 
stood by those not familiar with arithmetical expressions, is shown below. 

These rules are termed “Ohm’s Law” in honor of one of the early 
investigators of electricity. 

















8 


TELEPHONOLOGY 


V = Volts (Pressure) - - V V 

A = Amperes (Quantity) divided by or - 

R = Ohms (Resistance) A x R A R 

To use this method place the thumb over the quantity it is desired 
to find, for instance, suppose a battery o' three volts is used, and is 
passing a current through 10 ohms, how much current (amperes) is flow¬ 
ing? 

When thumb is placed over A the formula reads V divided by R, 
which is: 3 divided by 10 which equals .3 ampere, the amount of current 
flowing. 

Suppose a resistance coil measured 20 ohms and when an ammeter 
was placed in circuit a reading of 5 amperes was obtained, and the voltage 
is required. By placing thumb over V the formula reads A times R, or: 
20 times 5 equals 100 which is the voltage. 

Suppose a 3 volt battery is used, and one-half ampere is flowing, 
what is the resistance in circuit. By covering up R we have V divided 
by A, or: 3 divided by .5 equals 6 ohms. 

This law will solve any direct current problem. Provided two of the 
quantities are known, the third can always be calculated. 

It will be seen that if the resistance of a wire is decreased, more 
current will flow through it. This fact is observed in putting up a tele¬ 
phone line; as the resistance of the line can only be decreased by using a 
large wire, and owing to the cost, it is impractical to use wire exceeding 



Fig. 12. Fig. 13. 


a certain size. On the other hand, it will be seen that more current will 
pass through the wire if the voltage or pressure is increased, and this is 
what actually occurs when the battery and transmitter are used, as pre¬ 
viously described. 

When the two receivers alone were used a very weak current was 
created, depending upon the strength of the magnets. Since the trans¬ 
mitter has come into use a greater pressure is obtained by using the bat¬ 
tery, and the pressure of the battery is regulated by the action of the 
transmitter, as shown in Fig. 10. 

It would immediately occur to one that the only thing necessary to do 
in order to gain power sufficient for talking over any distance would 
be to increase the battery. This, however, cannot be done, owing to the 
fact that if too much power is used the granular carbon in the transmitter 
will burn up, the passage of electricity through the carbon heats it 
when the voltage is too high. 

Some means, therefore, had to be devised to increase the voltage with¬ 
out burning up the transmitter. This was finally accomplished by the use 
of the piece of apparatus known as the induction coil. 

If a current is passed through a coil wound upon one end of a rod of 
iron, as shown in Fig. 12, the latter will become a magnet. If another 


















FIRST PRINCIPLES—TALKING EQUIPMENT 


9 


coil of wire is wound over the first, whenever the current in the first coil 
is increased or decreased a corresponding current will be created in the 
second coil. This current will be weaker or stronger in proportion to the 
number of turns the second coil possesses in relation to the first. If the 
first coil had five turns of wire, and the second coil twenty-five, then the 
voltage in the second coil would be five times greater than that in the first 
coil. 

This can be better understood if we imagine that when a current is 
passed through the first coil the iron core becomes magnetized, and the 
lines of magnetic force spread out from the core, as shown in Fig. 13. 
As they spread, they encounter, the wire composing the second coil, which 
is usually wound over the first coil. This immediately generates a cur¬ 
rent in the second coil. If the current is decreased the lines shrink back 
into the core, and disappear. This back and forth action of the lines of 
force produce in the second coil of wire a current of electricity identically 
similar in its character to that in the coil producing it, and, as previously 
stated, if the number of turns of wire in the second coil are more than 
those in the first coil, the strength of the current created in the second coil 
will be greater. This fact is made use of by arranging the transmitter, 
induction coil and other apparatus as shown in Fig. 14. 

Comparatively few turns of coarse wire, known as the primary, are 
wound directly on the core of the coil. A couple of cells of battery are 
connected with the transmitter and primary, as shown, while the line 
wire and receiver are connected to the secondary, which consists of a great 
number of turns of wire wound directly over the primary. 

When the transmitter is spoken into, the current in the primary is 
increased or diminished, which causes a corresponding increase or dimin¬ 
ution of the lines of force created by the iron core. This affects the sec¬ 
ondary, causing a current of increased strength, and as an increase of 
voltage will always carry current through a greater resistance, enough 
current will pass over the line to operate satisfactorily the receiver, and 
induction coils are therefore used in all modern instruments. 



Fig. 14. 


The above parts of the telephone constitute all that are used in the 
transmitting and receiving of speech, and while the form, size, shape and 
other details of the parts may vary in different makes of instruments, the 
principles here given concerning their operation hold good for any type. 
There are many other principles entering into their construction which 
will be described later. 


























CHAPTER II. 


SIGNALLING EQUIPMENT. 


While we now have the means of talking from one point to another, 
it yet remains to devise some means of signalling, as the receiver itself is 
not sufficiently loud to call a person to the instrument, and some form 
of bell or other device is necessary. It would seem that an ordinary 
vibrating bell, commonly used for various purposes would also be selected 
for telephone work. This instrument is illustrated in Fig. 15, but it 
possesses many disadvantages which render it impractical for telephone 
use. The main trouble is the fact that the contact point shown at “s” is 
liable to spark, especially if sufficient battery is applied to ring the bell 
over a long line. 



RCY 


+ 



Fig. 15. 



When the key is depressed, current flows through the magnet wind¬ 
ings N. S. which attract the armature a. This moves toward the magnets 
breaking contact s, stopping the current flow. The armature springs 
back, contact s is closed, the current flows, the armature is again attract¬ 
ed. This continues as long as the circuit is closed. A gong, not shown in 
the figure, is so placed that the clapper rod will strike same at each 
impulse. 

As this instrument requires battery for its operation, it would be 
inconvenient to have a sufficient number of these at each telephone to 
ring the bells on the line. Some other form of signalling device is there¬ 
fore necessary. 

A telephone bell, as shown in Fig. 16, consists of two spools of wire 
wound on soft iron cores. The latter are connected together by means of 
a piece of soft iron at the bottom, while to this piece the permanent mag¬ 
net “N. S.” is connected, so that the top curves over the armature “A. A.’' 
which is a piece of soft iron suspended in the middle so that it is free to 

( 10 ) 























































SIGNALLING EQUIPMENT 11 

move. Attached to it by means of a rod is the ball “B”, adapted to strike 
the gongs G and G. 

The lines of force from the permanent magnet “N. S.” magnetize the 
soft iron armature so that it becomes a magnet. Instead of opposite 
magnetic poles being at each end of the armature, the ends of the arma¬ 
ture become, we will say, north poles, while the middle portion of the 
armature directly under the magnet becomes a south pole. 

The ends of the iron cores upon which the wire spools are wound 
also become south poles because they are connected to the south pole of 
the permanent magnet, apd form simply, an extension to same. 

The current from the .generator flows first in one direction and then 
in another through the two spools of wire, and this magnetizes the iron 
cores. The left hand core “C”, we will suppose, becomes the north pole, 
while the right hand core “C” .becomes the south pole. This being the 
case, the right hand pole will attract the armature directly above it, be¬ 
cause opposite poles of magnets always attract each other. 

While this is taking place the left hand pole, which is the south pole, 
will repel the armature directly above it, as like poles always tend to repel 
each other. This causes the ball to move toward and strike one gong. By 
this time the current from the generator has begun to flow in the oppo¬ 
site direction, and the operation is reversed, the left hand spool of 
wire causing its core to become a south pole, while the other spool causes 
its core to become a north pole. This attracts the armature in the other 
direction, which in turn, causes the ball to strike the other gong. 

It will now be seen that with every alternation of the current a move¬ 
ment of the armature to one side or the other is produced. 



Fig. 17. 


The machine for ringing telephone bells is called a magneto gene¬ 
rator and is shown in theory in Fig. 17. “N” and “S’ represent the ends 
of a permanent magnet. The circles placed within the centre opening 
known as the ‘‘field” represent a piece of wire looked at directly from the 
end. The wire really consists of many turns, and is wound upon an iron 
spool known as the armature, which revolves, and during each revolution 
the wire is placed successively in the twelve positions, shown in the draw¬ 
ing. 

Magnetic lines of force are flowing across the center opening from the 
north to the south poles of the magnet, as shown by the arrows, and at the 
instant the wire is in the position “0”, no current will be created in it 
















































12 


TELEPHONOLOGY 


because it is moving parallel to the lines of force, and no current is gener¬ 
ated in the wire when it moves with the lines, as it is always necessary to 
move the wire across them. 

As the wire revolves in the field it cuts across some of the lines, and 
at position “1” is directly at right angles to them. Here the greatest 
current is generated within it. The relative strength of the current 
created at each point during this process is shown by the light and heavy 
crosses placed within the circle representing the wire. 

A corresponding decrease in the current takes place from point “1” 
to point “2”, and when the wire reaches the latter point, it is again 
parallel to the lines of force, and, consequently, no current is generated. 

The same action takes place from point “2” to point “3”, where the 
wire is again at right angles to the lines of force, and the current created 
again reaches a maximum. A corresponding decrease takes place from 
“3” to “0”, this process being repeated during each revolution of the 
armature. 

While the wire is passing from the point “0" to “2”, a plus current 
or as it is termed, a positive current, is generated if the north pole of the 
magnet is on that side, while from the point “2” through “3” to “0”, 
a minus or negative current is generated because the wire is there subject 
to the influence of the south pole. 



Fig. 18. 

Plus current is represented by the sign -J-, and minus current by the 
sign —. Current flowing first in one direction and then in another is 
called alternating current and Fig. 18 illustrates waves of a current of 
this kind given by a magneto generator. On the left are figures represent¬ 
ing the voltage, while the points “0-1-2”, etc., along the curved lines repre¬ 
sent the different positions of the wire during one revolution, and corres¬ 
pond to those in Fig. 17. Starting at line “0” where there is no current, 
we will suppose that the upper curved line represents plus current, and the 
lower curved line, minus current. From this it will be seen that current 
from the telephone generator flows first in one direction and then the 
other, the voltage increasing from “0” to “1”, and then decreasing to 
“2”, as the wire at this point (see Fig. 17) is no longer cutting across the 
lines of force. The current then increases to “3” in the opposite direction, 
and again decreases to “0”. 

This operation of the current increasing from “0” in one direction, 
returning to zero and increasing in the other direction, and back to zero 
again, is called a CYCLE . 

A telephone generator gives one complete cycle of current for every 
revolution of the armature and generators are so geared that the armature 














SIGNALLING EQUIPMENT 


13 


usually makes 1000 turns per minute, or 5 times the speed at which the 
crank is turned. When revolutions are spoken of, it should be remember¬ 
ed that it is those of the armature which are referred to. 

A good three bar generator should give from 65 to 90 volts when 
turned at the regular speed. A four or five bar bridging generator, from 
75 to 110 volts. The quantity of current given by the bridging generator 
is much greater than that given by the series instrument. 

The voltage obtained is in proportion to the speed at which the 
armature is revolved. The faster the speed, the greater number of lines 
of force the wire on the armature cuts across, and the higher the voltage. 
This is the reason why turning the crank rapidly on a telephone will some¬ 
times enable one to ring a distant phone which will not ring when the 
crank is slowly turned. 

The FREQUENCY of an alternating current is the number of cycles 
in one second. 

An ALTERNATION is one half of a cycle. 

An alternation may be either POSITIVE or NEGATIVE. 

A CYCLE consists of,one positive and one negative alternation. 

As the frequency of an alternating current is the number of cycles 
passed through in one second, and as a telephone generator gives one 
complete cycle of current for every revolution of the armature, to find 
the frequency: 

Divide the revolutions per minute by 60. This gives the CYCLES 
per second. 

If you desire to find the alternations per minute: 

Multiply the cycles per second by 120, or if the alternations per 
minute are knoivn, to find the cycles, divide the alternations by 120. 

If the coil of wire in the telephone generator were simply revolved 
in the field, the resulting current would be very weak. The coil is there¬ 
fore wound on an iron core or “armature”, which concentrates the lines 
of magnetic force in the manner shown in Fig. 19. 



Fig. 19. 


This causes more of those lines to pass through the windings, and the 
strength of the current is thereby increased. 

A number of magnets are used, so arranged that all the north poles 
are on one side of the armature and the south poles on the other. 

Series generators usually have three magnets, and are termed three 
bar generators. The armatures are wound with a great number of turns 





14 


TELEPHONOLOGY 


of wire, and the resulting circuit has a high voltage but a small amperage. 

Bridging generators have from four to six magnets, and the arma¬ 
tures are wound with coarser wire. The current is of moderate voltage, 
while a considerable quantity is produced. 

The number of bars is no indication of the strength of the generator, 
this depending upon the cross section of the magnets. A generator with 
four magnets % x 1/2 in. square is stronger than one with six magnets 
l A x V 2 , in. 

When ringing a telephone bell, during one-half a cycle, or one alter¬ 
nation of the current, the ringer armature is attracted in one direction, 
and during the other half of the cycle the armature is attracted in the other 
direction. This process is continued as long as the generator crank is 
turned. 

The alternating current, as above described, can be made sufficiently 
powerful to ring a “magneto bell” as the telephone ringer is termed, 
over a considerable length of line, and we are therefore enabled to signal 
from one end of the line to the other. 

It now becomes necessary to devise some means of having the signal¬ 
ing equipment connected with the line in such a manner that a ter the 
signal has been given the bells and generator will be automatically dis¬ 
connected and the talking equipment connected to the line as the line 
must be free for talking purposes. The batteries must be connected 
to the transmitter, as they cannot be left on all the time. Various devices 
for doing this were devised. These consisted of switches, etc., and from 
them was finally evolved the present type of switch known as the “Hook”, 
or “Receiver Hook”. 

The hook controls the various circuits connecting or disconnecting 
them from the line. In early types of hook switches a great deal of trouble 
was caused by loose connections, in the modern hooks this has been 
entirely eliminated. 

The Sumter Hook Switch shown in Fig. 19a illustrates the modern 
construction of this part. A steel stamping forms the body upon which 
all the other parts are mounted. By means of two screws passing through 
the telephone box, the hook is secured in position and is entirely self- 
contained, thus eliminating the trouble found in early types where the 
springs were mounted on one side of the box and the hook on the other. 
When the wood warped or a screw loosened the parts changed their 
relative position and no longer operated properly. 

All danger of loose contacts has been eliminated in the type of hook 
shown in Fig. 19a, by using long flexible springs with riveted contact 
points of platinum. 

When the springs are assembled they are given a downward tension 
which brings them to rest against the rubber rollers as shown. These 
rollers adjust the relative position of the springs very accurately. From 
this it will be seen that the position of the springs is not dependent upon 
the elasticity of the metal but each spring is held under tension. 

The rollers act to bring the springs together with a biting motion 
which puts a pressure of several pounds on the contact points. 

One weak point in a great many hooks is the use of some imitation of 
rubber for insulation between the springs. Nothing but pure hard rubber 
should be used and this should be as thick as possible to guard against 
lightning punctures. 


SIGNALLING EQUIPMENT 


15 


In some hooks the tension of the contact springs is relied upon to raise 
the hook lever. This sometimes causes the contact spring to weaken and 
fail to operate properly. In the Sumter hook a separate raising spring 
is used, made of round steel. This is placed on the rear side of the hook 
base and is locked on two pins from which it can be instantly removed 
if necessary. This spring is enameled to prevent rust. 

The escutcheon plate is held in position on the telephone instrument 
by two machine screws which also hold the hook in the telephone box, 
as shown. The hook which is a heavy stamping from sheet brass, nickle- 
plated, is inserted through the escutcheon plate and clamped to the hook 
by means of a heavy steel set screw. The escutcheon plate does not limit 
either the upward or downward motion of the hook lever, this being taken 
care of by a permanent adjustment forming part of the hook base itself. 
It is therefore unnecessary to pay any attention to the adjustment of the 
travel of the hook lever, this adjustment being taken care of in the assem¬ 
bling of the hook parts and cannot be changed by any wear in the hook 
itself. 

For shipment or in case of breakage, the hook lever can be withdrawn 
from the hook by simply loosening the cap screw and pulling the lever out. 

In some types of hooks the lever is made instantly removable by 
unlatching same, a catch or other means readily operated by the finger 
being provided. 



FIG. 19a. 


Fig. 19a shows a hook for bridging telephones. The three springs 
close when receiver is off the hook lever. For series work anothei spring 
is required, so placed that when the receiver is on the hook, two of the 
springs will be in contact, this contact being broken when receiver is 
off and the three springs closing together same as in the bridging, leaving 
the extra spring not in contact with anything. 

All modern hook switches are so arranged that the hook lever and 
metal parts of the hook body are insulated from the contact springs 
carrying the circuit of the instrument. This prevents the user at the 
phone receiving a shock from touching the hook. 

A simple diagram of the telephone with the hook and necessarv 
signalling and talking equipment is shown in Fig. 20. 

The instruments are in the signalling position when the receivers 
are on the hooks, and the bells and generators are so connected that if 
the crank on one of the generators is turned, a current will pass over 
the line through the bells and back again. 



16 


TELEPHONOLOGY 


After the signal has been given, if the receivers are removed from the 
hooks, the hook lever moves upward and closes the top contacts, so that 
the transmitter batteries are placed in circuit, the receivers and induction 
coils are connected with the line, and the generator and bells in each 
instrument are cut off, leaving the line entirely free for talking purposes, 
as the bottom contacts shown dotted, are broken as soon as the receivers 
are removed from the hooks. 

We have considered the apparatus necessary to transmit speech and 
signals over the line. There are two ways in which telephones may be 
connected: in series, and in multiple or “bridging”. A series circuit 
consisting of three telephones is shown in Fig. 20. 

If a telephone on one end desires to call the telephone on the other, 
upon turning the generator crank, the bells in all three instruments will 
ring. By having a different ring for each phone, any of the three can be 
called at will. 

If the two end phones remove their receivers from the hooks they 
can talk together, the voice currents passing over the bottom line and 
returning over the top line in the figure and passing through the ringer 
coils at the middle ’phone. If there were other telephones on the line 
the current would also have to pass through the ringer coils of each one. 

The series method is perfectly satisfactory when there are only two 
telephones on the line, as the ringers are not in circuit when the receivers 
are off the hook, but when there are more than two instruments on the 
line it is necessary for the voice currents to overcome the resistance of 
the fine wire wound on the ringer coils in all the instruments on the line 
except the two in use. For instance: when the end instruments in Fig. 
20 are speaking together, the voice currents must pass through all the 
fine wire on the ringer at the middle ’phone. 



Another serious objection to the operation of series circuits is what 
is termed “self-induction” or impedence, which is illustrated in Fig. 21. 
Here a soft iron core is shown upon which is wound a number of turns 
of wire. When a current is sent through the wire, it passes around the 
core, and at every one of the turns it induces or creates in the turn of 
wire next to it a current which moves in the direction opposite to that 
of the first. This reacts upon the main current, and tends to check or 
impede its progress. In this way a current will react upon itself, and its 
progress through the coil will be hindered. This reaction is called self- 
induction. 

The self-induction of a coil depends directly upon the number of 
turns oi wire and upon the strength of the passing current together with 




















SIGNALLING EQUIPMENT 


17 


the amount of iron in the core. As a ringer coil possesses a great many 
turns, the self-induction is very high, and the voice currents are hindered 
much more in their passage by an 80 ohm ringer than they would be by 
80 ohms of straight wire, which possesses no self-induction. 

Just as the unit of pressure of electricity is termed a volt, the unit 
of self-induction is termed a “Henry.” 

The phenomenon of self-induction is principally exhibited in connec¬ 
tion with alternating currents. The effect of self-induction upon the 
transmission of voice currents is similar to resistance. The “inductance” 
of a coil is measured in Henrys by the number of volts of Counter Electro 
Motive Force generated when the current changes at the rate of one 
ampere per second. 

The ringer coils of telephones have an inductance varying from one 
to seven Henrys, while generators vary from two to ten Henrys. Tele¬ 
phone receivers vary from fi ty to one hundred and twenty-five mili- 
Henrys, a milli-Henry being the one-thousandth part of a Henry. 


1 — 

1 — 1- 

=3 

Current- \ 

ente.rtnfj Coil 


1 Cort,. 

Triducedi . 'l 

G<jrre.OT. t 



cz 

-trrr 

=1 


Fig. 21. 


The resistance due to self-inductance equals 6.2832 multiplied by 
the frequency of the current times the Henrys. 

To illustrate this we will suppose that a coil has an inductance of 
5 Henrys. The frequency of the current is 60 cycles per second. Multiply 
6.2832 by 60 and the result equals 365.1920 times 5, equals 1884.961 ohms. 

From this it will be seen that a ringer possessing an inductance of 
5 Henrys will offer a resistance of over 1800 ohms to the passage of an 
alternating current at a frequency of 60 cycles per second, and as. voice 
currents have a frequency ranging into the thousands, the opposition of 
the coil to the passage of such currents is very great. 

It should be remembered that the resistance due to self-induction is 
plus the ohmic resistance of the coil. For instance: if a coil possessing 
a resistance of 1884 ohms, due to self-induction, measured 1600 ohms 
ohmic resistance, the total resistance the coil would offer to a 60 cycle 
current would be 3488 ohms. 

From the above it will be seen that it is impractical to put many 
telephones in series, as the result of the self-induction of the ringer coils 
is to render the speech very indistinct and unsatisfactory. 

Another serious objection to the series circuit is the fact that the 
voice and ringing currents must pass through all the bottom hook contacts 
of the different telephones on the line. This is shown in Fig. 20. In case 
the hook fails to make proper connection the entire line is out of service, 
and it is sometimes very difficult to locate just where the trouble is, a 
visit to every telephone on the line often being necessary, and it is gener¬ 
ally the case that the trouble is found to exist in the very last instru¬ 
ment visited. This trouble was eliminated to a certain extent by wii ing 
2 









18 


TELEPHONOLOGY 


the instrument as shown in Fig. 22. When this is done the instrument 
will ring in case the bottom contact is bad, for the ringing current will 
pass through the receiver and secondary of the coil and then through 
the ringer in the ordinary manner. The trouble due to self-induction 
and resistance of the ringers still remains, however, and for this reason 
series lines are rapidly going out of use. 



Three telephones connected on a bridging circuit are shown in Fig. 
23. The principal difference between this and the series circuit already 
noted is the fact that the different bells and generators are bridged across 
the line like the steps of a ladder, instead of being in series with the lines. 



The generator in a series instrument is equipped with a set of shunt 
springs, so that except when the crank is turned the winding of the 
armature is short circuited, and offers no resistance to the passage of 
the current. This is necessary to remove the resistance of the armature 
from the circuit. 

In bridging instruments the reverse of this is done. The generator 
armature, instead of being short circuited is open all the time except 











































































































SIGNALLING EQUIPMENT 


19 


when the crank is turned, in which case the axle moves inwardly and 
connects the generator to the line. 

In bridging instruments advantage is taken of the impedance of the 
ringer coils, which are wound with a great number of turns of wire and 
are o! high resistance. They therefore offer an enormous resistance to 
the passage of the high frequency voice currents. When either of the 
end telephones calls the other, (Fig. 23) the voice currents will pass 
oyer the line from telephone to telephone, and will not pass through the 
ringer coils of the middle, phone at all on account of its high ohmic 
resistance and impedance. 

Another desirable feature in bridging instruments is the fact that 
there need be no bottom hook contact and the bells can be left always 
connected to the line wires which reduces the number of springs in the 
hook to those necessary for connecting the receiver and transmitter 
circuits. 

From the above it will be seen that self-induction which is a hind¬ 
rance in series work, is of great advantage in bridging service. 
Bridging ringers are therefore wound so as to possess as high self- 
induction and resistance as possible. 1600 ohms is generally accepted 
as the standard winding for bridging ringers. As the number of turns 
of wire determines the impedance, it will be apparent that simple ohmic 
resistance is not all that is necessary, and when extremely fine wire, 
such as is used in 2000 and 2500 ohm ringers is used, the actual number of 




turns is somewhat reduced, as it has been found that a 1600 ohm ringer 
possesses a maximum of self-induction together with ohmic resistance. 

The generators used in series and bridging work differ, as generators 
used in series work must be designed to deliver current of high voltage 
to force the current through all of the bells on the line, whereas generators 
designed for bridging work need not possess very high voltage, but must 
give a quantity of current sufficient to move all the ringers, as the 
current divides, a little bit passing through each ringer on the line. 

The difference between series and bridging circuits, both as to talking 
and ringing is well illustrated by Figs. 24 and 25. By reference to Fig 24 
which represents a bridging circuit, it will be seen that the water in the 
upper pipe subdivides, one third of the water flowing through each of 
the wheels, the return pipe taking it to the receiver tank. The pump in 
this illustration representing the hand generator, while the water acts 
in exactly the same manner as the current given forth. In Fig. 25 a series 
arrangement of the wheels is shown, and the water must flow through 
all of the wheels to get back to the receiving tank. It will be seen that 
a sufficient quantity of water to move all three of the wheels is necessary 
in the bridging arrangement, while a smaller quantity of water having a 
high pressure, will do the work in the series arrangement. 
































20 


TELEPHONOLOGY 


It will also be seen that in the series arrangement, if one of the 
wheels becomes inoperative, the water could not flow through any of the 
wheels, while in the bridging arrangement if one of the wheels should 
cease to move, it would in no way affect the other two. 

The actual resistance of an 80 ohm ringer to voice currents is approxi¬ 
mately equal to 50,000 ohms. It will thus be seen that the two end sub¬ 
scribers on a series line of three instruments are obliged to talk through 
50,000 ohms resistance in addition to the line resistance. 

In the bridging arrangement a bell of 1000 ohms resistance possesses 
an impedance of much more than 50,000 ohms. It will thus be seen that 
any loss due to leakage through the ringer between the two end parties 
on a bridging line of three instruments is infinitesimal. 



Fig. 26. 


A standard telephone ringer is shown in Fig. 26. The side rods 
support a yoke in which is pivoted the armature, to which is connected 
the striker rod and ball. The permanent magnet is securely fastened to 
the cross piece to which the coils are fastened, and curves upward over 
the armature which it magnetizes. 

The distance of the armature from the pole pieces is readily adjusted 
by turning the nuts on the side rods up or down. In the type of ringer 
shown in the figure as additional adjustment is provided by tapping the 
end of the magnet and inserting a screw, which can be turned while the 
bell is ringing, this springs the cross yoke carrying the armature, and the 
proper distance of the armature from the pole pieces can be accurately 
obtained. On long and heavily loaded lines the armature may be brought 
very near the pole pieces. This shortens the stroke of the clapper, and 
the gongs must be brought near together, or the clapper ball will not strike 
them. 

The accurate adjustment of the distance between the gongs is im¬ 
portant. The method of obtaining this varies in different ringers, but 
the common method is to fasten lugs to each bell post with slots cut in 
them, in which screws are fastened in such a manner that the posts can 
be clamped in various positions. The clapper should hit each gong and 
spring back. At rest on each side, it should be about l-64th inch away 
from the gong. 

The use of telephones in which the ringer gongs are mounted upon 
the wooden door of the instrument should be avoided. If the wood 






























SIGNALLING EQUIPMENT 


21 


shrinks it will change the adjustment of the bells, and thereby render the 
instrument inoperative. 

The length of the clapper rod plays a considerable part in the sensi¬ 
tiveness of the bell. A short rod will produce a weak but sensitive stroke 
which insures the instrument ringing, but the ring will not be very loud, 
while a long rod will secure a powerful stroke, but the bell will not be 
as sensitive. 

The only difference between series and bridging ringers is the length 
of the wire coils. The exact dimensions as used by one manufacturer 
for a series ringer coil are shown at “A”, Fig. 27, while a bridging coil 
is shown at “B”. The heads are 1 1-16 inch dia. A series winding may 
be of 80 ohms resistance, which gives very satisfactory results when a 
number of series telephones are used on one line. This is no longer done, 
the principal use to which series instruments are now put being local 
exchange service, in which case the ringers should be wound to 250 or 
500 ohms resistance. If ringers of low resistance are used, when two 



telephones are connected through the switchboard by means of an ordi¬ 
nary cord circuit in which the clear-out drop is bridged, the clear-out drop 
will be short-circuited by the low resistance ringers, and the drop will 
not operate perfectly when the ring off signal is given. If the ringers 
are wound to a resistance of 250 ohms no trouble from this source will 
be experienced. 

Standard series and bridging windings on the size cores shown in 
Fig. 27, are given in the accompanying table. 


One coil for 


Turns 


B. & S. Gauge 
Single silk Ins. 


Layers. 


250 ohm ringer 

3360 

33 

32 

1000 ohm ringer 

8640 

35 

34 

1200 ohm ringer 

8096 

36 

32 

1500 ohm ringer 

9108 

36 

36 

1600 ohm ringer 

10160 

36 

40 

2000 ohm ringer 

11520 

36 

48 

2500 ohm ringer 

13440 

36 

54 


Resistance, 

ohms. 

125 

500 

600 

750 

800 

1000 

1250 


*“To the average electrician who wishes to find the proper size of 
wire to use in the windings of electromagnets, the use of winding formula? 
is often confusing. The graphic system, however, not only eliminates the 
necessity of formula?, but makes the whole operation clear and simple. 

In describing each of the accompanying charts actual cases will be 
cited to facilitate following the methods employed. No reference will be 


*Chas. R. Underhill in Am. Electrician. , 
















22 


TELEPHONOLOGY 



i 


IT 


AmuEl*. 




Fig. 28. 

made to the theory of the electrical constants or how the charts are made. 

In order to find the proper size of insulated copper wire to fill a given 
winding space, and have a given resistance, it is necessary to know the 
cubical contents of the bobbin, or the actual volume of the winding space 
in cubic inches, and the ohms per cubic inch for the various sizes of 
copper wire with various increase in diameters due to the insulation. 



Fig. 29. 

































































































SIGNALLING EQUIPMENT 


23 


Therefore, if the winding volume of a bobbin be 2 cubic inches, and the 
ohms per cubic inch 250, the resistance of the winding would be 500 ohms. 
It is very important that the actual available winding space should be 
taken; that is, the space which is left after the bobbin is properly insulat¬ 
ed. 

As most windings for electromagnets are wound upon a round core 
or tube, the round type of bobbin will be assumed throughout this article. 
This bobbin is illustrated in Fig. 28. 

Referring to Fig. 29 the winding volume (in cubic inches) per inch 
of length of winding is found by following the curved line, which starts 
i rom the value of d, the inside diameter, to where it intersects the horizon¬ 
tal line corresponding to the value of D, the outside diameter, and then 
tracing vertically downward. 



As an example, the outside diameter of a winding is 2 inches and the 
diameter of the insulted core, d, is .9 inches. Following the curve which 
starts at .9 it will be found that it intersects the horizontal line correspond¬ 
ing to 2 at the vertical line corresponding to 2.5 cubic inches per inch 
of length of winding. If the length, L, be 3 inches the volume of the 
winding will then be 2.5 X 3 = 7.5 cubic inches. 



diameters of copper wire irrespective of the gauge number, with various 




































































































































































































24 


TELEPHONOLOGY 


increase in diameter due to insulation. A 4-mil increase means that the 
diameter of the insulated wire measured over the insulation, is 4 mils 
greater than the diameter of the bare copper wire. For convenience, the 
different sizes of wire of B. & S. gauge are shown in dotted lines, in posi¬ 
tions corresponding to their diameters. 

Although the increase in diameter due to insulation on the wire may 
vary with different manufacturers, the increase in diameter due to single 
silk insulation varies from 1.5 mils to 2.5 mils, and from 3 mils to 5 mils 
for double silk insulation. For cotton-covered wire the increase in diam¬ 
eter varies from 4 to 5 mils for single cotton, and from 8 to 10 mils for 
double cotton insulation. In any event it is well to caliper the insulated 
wire with a rachet stop micrometer, to ascertain the increase in diameter 
due to the insulation. 



O O *0 »Q lO f . O . O 

ci «i CO C5 •'J* -r <» *o lO to i-'’ JO ad & s 9 m H 

OHMS PER CUBIC INCH Am.rEl.c 


Fig. 32. 




























































































































SIGNALLING EQUIPMENT 25 

As an example of the use of these charts, refer to Fig. 32 and assume 
that an insulated copper wire is desired which shall have a resistance of 
4 ohms per cubic inch when wound on a bobbin. Tracing vertically 
u P 1 J a . r ^ f r . om 4 it will be found that this result is obtained with a wire 
.018 inch in diameter, with 8 mil insulation, or with a wire .0184 inch in 
diameter with 7 mil insulation, etc., the largest diameter of copper being 

obtained with 1.5 mil insulation, the diameter of the wire being 0208 
inch. 

Therefore, if the 8-mil insulation be used a No. 25 B. & S wire would 
be used, while with even 3-mil insulation a No. 24 B. & S. wire would 
suffice, this latter wire being desirable.f 



Likewise, if the bobbin will contain 1.24 cubic inches of wire, and a 
resistance of 500 ohms in required, it is evident that an insulated wire 
with 4050 ohms per cubic inch would satisfy this condition, and by refer¬ 
ring to Fig. 35 it is found that No. 40 B. & S. wire with 1.5-mil silk 
insulation will meet this requirement. 



Fig. 35. 


See “Comparison of Common Methods of Coil Windings,” American Electrician, 
May, 1905. 







































































































































































































































26 


TELEPHONOLOGY 


The following cases will aid in approximating coils: 

Case 1 .—Given a bobbin with dimensions D = 3, cl = 1.5, L = 3.25 
resistance 500 ohms, to find proper size of wire with 4-mil single cotton 
insulation. 

Referring to Fig. 29 it will be R)und that there will be 5.25 cubic 
inches per inch of length of winding which makes the volume of the wind¬ 
ing 5.25 X 3.25 = 17.06 cubic inches. The ohms per cubic inch 
will then be 500 17.06 = 29.3. Reference to the charts will show that 

the nearest copper wire with 4-mil insulation will be No. 29. 

Case 2 .—If No 30 B. & S. 4-mil insulatecj wire were used in the above 
will then be 500 17.06 = 29.3. Reference to the charts will show that 

side diameter of the winding, all other dimensions remaining the same? 

Referring to Fig. 33, it will be found that the ohms per cubic inch 
are approximately 44 for No. 30 B. & S. wire with 4-mil insulation. 
Therefore, the volume of the winding must be 500 44 — 11.4 cubic 

inches, since the length of the winding is 3.25 inches the winding volume 
per inch of length will be 11.4 -r- 3.25 = 3.5. Referring now to Fig. 29, 
and tracing vertically upward from 3.5 to the point where this line inter¬ 
sects the curve which starts from 1.5 the outside diameter, D, is found 
to be 2.58 inches. There'ore, wind to a diameter of 2.58 inches, with 
No. 30 B. & S. wire with 4-mil cotton insulation, and the resistance will 
be approximately 500 ohms. 

While other cases may be worked out for any given diameter of wire 
and any increase due to insulation, the two cases above given are the most 
used, and after a little practice these problems may be very easily worked 
out.” 

With the majority of ringers, some tool is necessary to adjust the 
position of the armature in relation to pole pieces. For instance, with 
the type of ringer shown in figure 26, long used by the Bell and many 
independent companies, the cross yoke holding the armature in front of 
the pole pieces is mounted on two side rods, the yoke being clamped between 
two nuts on each rod. To adjust the armature, it is necessary to move 
these nuts up and down, and thereby increase or diminish the distance 
between the armature and the pole pieces. In the majority of ringers 
now sold the adjustment of the armature is accomplished in this manner. 

There are a number of ringers on the market in which the position 
of the armature is permanent, while the pole pieces have threaded exten¬ 
sions which can be turned up or down, thus increasing or diminishing 
the space between the pole pieces and the armature. When oroper 
adjustment is secured, these extensions are clamped by means of thin 
fiat nuts. 

With a view to securing a ringer that could be adjusted without the 
use of any tools, the type shown in figure 36 was developed, which may 
be taken as typical of modern ringer equipment. 

The various parts are assembled in the standard manner, the gongs 
being mounted on posts which are adjustable by means of machine screws. 
After the gongs are once set, and this is usually done in the factory, they 
seldom require adjustment, and in this particular ringer, owing to the 
shape of the gongs and the adjustment of the various parts, all necessary 
readjustments when the ringer is in service can be accomplished by 
moving the armature up and down. 


SIGNALLING EQUIPMENT 27 

The armature is mounted upon a cross yoke of spring brass, which 
has an initial upward trend holding the armature away from the pole 
pieces. A stem passes through this cross yoke down to the supporting 



Fig. 36. 


plate of the ringer frame. At the upper end of this stem is the adjust¬ 
ing wheel. 

By turning this wheel, the cross yoke holding the armature is brought 
nearer to or further away from the pole pieces. 

The adjusting wheel can be turned with the fingers alone as shown 
in Fig. 37, thereby adjusting the ringer while in actual operation. 



Fig. 37. 


On long and heavily loaded lines where a very careful adjustment is 
required, and when the wheel should only be turned a very minute dis¬ 
tance, any object such as an ordinary nail or key can be inserted in the 
slots of the adjusting wheel, and the wheel turned very slightly. This 
fine adjustment is shown in Fig. 38. 







28 


TELEPHONOLOGY 



Fig. 38. 

After making the adjustment in the manner above described it is not 
necessary to lock the wheel in any manner as it is so placed in relation 
to the other parts that it is held firmly under tension, and cannot itself 
turn, or get out of adjustment. The operation of the ringer has no 
tendency to change the adjustment, and therefore same is entirely perma¬ 
nent. 

By turning the adjusting wheel all the way up and removing the 
screws from the magnet and coils, the various parts of the ringer may be 
disassembled as shown in Fig. 39. 

The coils can then be easily removed, as there are no stamped punchings 
forced around the ends of the pole pieces, nor are the coils used to support 
any of the other parts, as they are simply attached to the ringer frame by 
means of screws. 

It would seem that this method of construction possesses some 
mechanical superiority over many older types, and it may be said that a 



Fig. 39. 

distinct gain in electrical efficiency is secured, inasmuch as the iron parts 
of any ringer are subject to a magnetic reversal which takes place during 
each revolution of the generator armature, and the more iron parts, the 
less sensibility the ringer will possesss. In this ringer all side rods, iron 
posts and other parts are eliminated, with the exception of the small 
adjusting wheel which is purposely made of soft iron, and this is placed 
directly between the end of the magnet and the armature itself, and serves 









SIGNALLING EQUIPMENT 


29 


to conduct the magnetic lines of force directly from the magnet to the 
armature,, thus magnetizing same to a greater degree than has heretofore 
been possible. This secures a maximum of efficiency and a distinct gain 
in sensibility and strength of stroke has been noted, due to this method of 
construction. 

A very unique method of assembling a ringer is used by the Sweedish 
American Tel. Co. This ringer is shown in Fig. 40. The magnet is 
mounted between the coils and it is claimed, a more uniform distribution 
of the. magnetic lines results from this method of assembly. A screw 
is put in each end of the armature, adapted to strike upon the cores of the 
coils. . These screws are iron with small brass tips and really form an 
extension of the armature. By turning them up or down, the armature 
adjustment is accomplished. 

This method of assembly makes a ringer of compact and efficient 
design. 



Fig. 40. Fig. 41. 


The majority of ringers in use are of the double coil type. Several 
types of ringers having only one coil have been developed. Typical of 
these is the ringer shown in Fig. 41 

The armature is pivoted at tne bottom end while the top forms the 
striker rod. The coil is hollow and the armature passes through the 
center of the coil. A magnet is used, shaped as shown. When current 
flows through the coil the armature, which really forms the core, is mag¬ 
netized, first in one direction and then in the other. This causes it to 
be attracted by first one and then the other of the magnet poles. This back 
and forth motion rings the bells in the usual manner. 

For ordinary exchange service, one phone or a line, this type of 
ringer would seem to be entirely satisfactory, but for bridging line service, 
it would seem to possess the objection of not having sufficient impedance, 
owing to the absence of a core in the coil, the armature not being nearly 
as large in cross section as a proper core. Another objection is the fact 
that to get a high resistance winding on one coil, the wire must be very 
fine, and therefore more liable to break downs and other troubles. 

To adjust the armature, adjusting screws are placed as shown in the 
figure. These however only limit the stroke of the armature, and do not 
bring it nearer to the magnet. The gongs are rigidly mounted on the 
cross 3 r oke and no means for adjusting them are provided. 













































30 


TELEPHONOLOGY 


Another single coil ringer in which the objection of no core is obvi¬ 
ated, is shown in Fig. 42. 

Here the coil is provided with a core, a U shaped magnet is used, and 
the armature is mounted over the core and magnet as shown. When 
current passes through the coil the armature is attracted alternately by 
the poles of the magnet as previously described. 

Another type is shown in Fig. 43. The core of the coil forms the 
armature. The entire core and coil are pivoted at the bottom as shown 
and swing freely between the two pole pieces. By means of nuts on each 
pole piece, extension ends are adjusted so as to limit the swing of the mov¬ 
ing parts. 

By making this ringer with a larger core and long winding, sufficient 
impedance is secured. The wires leading into the coil are coiled in small 
spirals thus making them flexible. 



Fig. 42. Fig. 43. 

Compared with the double coil type, none of these types have ever 
come into extended use, although they possess advantages as to size and 
simplicity in construction. These types are of comparatively recent 
design and may prove of value to the trade when more fully developed. 

In winding ringers it is customary to solder a comparatively coarse 
wire to the wire with which the ringer is to be wound. Then wrap tissue 
paper on the splice and begin winding. Before the first layer is put on, 
cover the core with paper. 

It is very bad practice to wind the ringer spool in any old fashion, 
as it renders it more liable to short-circuit and the efficiency of the instru¬ 
ment is reduced. The wire should be wound in smooth layers. 

Ringer coils intended for instruments to be used in mines and other 
damp places should be covered with shellac or paraffine. It is also advis¬ 
able to shellac the generator armature. Instruments of this class require 
careful winding and treatment along this line. 

In theory the coils of ringers and receivers should be wound in oppo¬ 
site directions. That is: if one coil is wound from left to right, the other 
coil is wound from right to left. This would be impractical from a 
manufacturing standpoint, as it would require “right and left” coils and 
cause confusion. In actual practice the inside ends of the coils which 
are both wound in the same direction are connected together, which 
accomplishes the same results. Particular attention should be paid to 
this fact. It does not matter which direction a pair of coils are wound 
in as long as they are both wound the same way, and both inside or outside 
ends are joined together. Do not join one inside and one outside end. It is 
better to connect the inside ends together and leave the outside ends to 
be connected to the wires in the telephone: for, in connecting the ringers, 




























SIGNALLING EQUIPMENT 


31 


in case the outside ends should become broken, a few turns can be wound 
off and the coils can again be connected, whereas if the inside end was 
broken, it would be necessary to re-wind the entire coil before it could be 
used. 

In removing the coil from the ringer frame, or when replacing same, 
make the screw connection between the ringer core and frame as tight as 
possible. This is necessary not only to have it tight, but also from the 
standpoint of securing greater electrical efficiency. 

It is well to sand paper the end of the core and yoke to which it is 
connected. 



It should be remembered that all ringer^ on the same line must be 
of the same resistance. This applies particularly to bridging circuits, 
and when re-winding ringer coils be sure that you use the same gauge wire 
as that which is taken off. The insulation should be the same. The 
gauge can be decided by securing a wire gauge, as shown in Fig. 44 and 
gauging the old wire. The kind of wire used for winding ringers comes 
on small spools which can be secured from the manufacturers, and by 
procuring one of the winding machines shown in Fig. 45, the exchange 
manager is well equipped for re-winding ringer and other coils. 



Fig. 45. 


It is almost needless to say that a duplicate set of ringers of various 

resistances corresponding to those in the telephones in use should always 

, * 













32 


TELEPHONOLOGY 


be kept on hand, so that in case of an accident to a ringer in use, the 
trouble can be remedied by taking out the damaged ringer and substitut¬ 
ing the duplicate. By observing this method, the subscriber will be 
pleased that his instrument is not out of service as long as it would be 
if the duplicate ringer had not been at hand. The damaged coil can be 
repaired at leisure. 

It will be noticed that spools for 250 ohm ringers are marked “125 
Ohms”. The 250 ohms is the total resistance of the entire instrument. 

A bridging ringer of 1600 ohms consists of two spools of 800 ohms 
each. Ringers for bridging work should possess great self-induction, 
which is obtained by making the cores long and shallow, and winding 
them with comparatively coarse wire. Resistance in itself is not desira¬ 
ble, but when the number of turns is increased the resistance is also in¬ 
creased. A ready means of distinguishing bridging and series ringers 
is by the length of the spools, the bridging spools always being longer. 

Series ringers are usually tested by ringing them through a resistance 
of 10,000 ohms or more. A series ringer with an ordinary 3 bar genera¬ 
tor in good order that will ring through a resistance of 10,000 ohms is 
in a satisfactory condition. An excellent test for a 1000 ohm ringer 
would be to connect the ringer, generator and a shunt coil, as shown in 
Fig. 46. Suppose the ringer to have a resistance of 1000 ohms and the 
generator to be a good 4 bar instrument, then the shunt coil “S” would be 
40 ohms. When the generator is turned at the usual speed, the current 
which passes through the ringer may be considered equal to the amount 
of current which would pass if this ringer and 25 others of the same 
resistance were connected on one line. 

It will be seen that this affords a rough method of adjusting ringers 
in the exchange before they are taken out and put on the line, while the 
operative efficiency of different makes of ringers can also be tested. 




rOZJ 


/•••* 


Fig. 46. 


If ringers of make “A” will ring perfectly with a 40 ohm shunt, 
while ringers of make “B” fail to operate, it will be seen that “A” is the 
best instrument, and by making the shunt “S” variable, it may be stated 
that the best ringer is the one that will ring with the lowest possible 
resistance in the shunt “S”. 

This method of shunting bridging ringers is to be preferred to test¬ 
ing them to ring through a given resistance, as the high resistance is not 
always at hand, while the 40 ohm resistance can easily be made from some 
wire from an old ringer or induction coil. 

These tests are very rough and serve only to approximate the 
efficiency. All tests of this nature are comparative: there is no standard. 

It will be seen from Fig. 20 and 23, Pages 16 and 18 that quite a 
difference exists in the calculation of the resistance of series and bridging 
circuits. In Fig. 20 a series circuit of three telephones is shown. Sup¬ 
pose these instruments to have ringers of 80 ohms resistance, the total 















SIGNALLING EQUIPMENT 


33 


resistance of the circuit through which the ringing current would pass 
is 80 multiplied by 3, which equals 240 ohms. 

In Fig. 23 a bridging circuit of three telephones is shown. We 
will suppose the ringers in this case to possess a resistance of 1000 ohms 
each. Here, instead of a total resistance of 3000 ohms, which would be 
the case in the series arrangement, it is one third of the resistance of 
one ringer, or 333 ohms. 

From this it will be seen that to calculate resistance from one side 
of the line to the other in a bridging circuit, when all the ringers are the 
same it is simply necessary to divide the resistance of one bell by the 
number of bells on the line, while in the case of series circuits, with all 
bells alike, multiply the resistance of one bell by the number of bells on 
the line. 

The foregoing measurements do not take into consideration the resist¬ 
ance of line wires. 

If a line with 3 series telephones on it was 10 miles long and the 
wire of which same was composed measured 50 ohms per mile, there 
would be an additional resistance of 500 ohms which would be added to 
the resistance of the ringers which equals 750 ohms, which would make 
a total of 1250 ohms. 

*‘Tn calculating the combined resistance of a line of bridged ringers 
a different condition exists. This then becomes a problem in resistance 
in which several resistances are in parallel, combined with some in 
series. If the line wires do not have a resistance, then the three instru¬ 
ments located at B, C and D, Fig. 47, would be considered as ordinary 
resistances in parallel, and consequently their magnitude would be deter¬ 
mined by the equation: 


1111 


R R, + R, + R, 


where R is the resulting resistance, and the others are the resistances of 
the respective instruments. In this particular case this formula reduces 
to the following: 


R, R 2 R 3 


R = 


R, R 2 + R, R 3 + R 2 R s 



Fig. 47. 


in which, if we substitute the value of the resistances as 1600 ohms each, 
we get a resultant R 5333.3 ohms. 

The line wires, however, are in series with the resistances, and these 
circuits must be taken into account. The current sent out on the A side 


*Sound Waves. 









34 


TELEPHONOLOGY 


of the line from the central office, divides at B, part of it going through 
the resistance of the instrument at that place, and part of it continuing 
on through the rest of the circuit. At C the current again divides, going 
through the remaining two branches of the circuit. In order to com¬ 
pute the resistance of this circuit, we begin at CC\ The resistance as 
measured between these two points consists of the two coils located at C 
and D, together with the two miles of iron wire connecting these two 
places. The resistance of C to C’, as measured around through Dl) 
is equal to 1666.6 ohms, it being the resistance of the coil at DD’ plus the 
resistance of the two iron wires, each having a length of one mile, and 
a resistance of 33.3 ohms. The resistance from C to C\ through the 
instrument, is 1600 ohms. Combining these two resistances in parallel as 
given by the first formula above, we get the following: 

1.1 1 

_ —-1-R = 816.6 

R 1600 16666.6 

Now the resistance as computed from B to B’ consists of this resist¬ 
ance just computed above, considered as being in parallel with the resist¬ 
ance of the first instrument. The resistance of B to B’ by the way of 
CC’ is equal to the resistance between CC’ or 1600 ohms combined with 
resistance just computed added to the resistance of two miles of wire, or 
1600 ohms combined with 816.6 + 66.6 ohms. 

Considering this latter resistance in parallel with the instrument BB’, 
we again use the formula above, and compute the resistance of BB’ as 
follows: 


111 

— = - -f - R = 569.1 ohms. 

R 1600 882.2 

We have now computed the resistance of the circuit as measured 
across the point BB’. Add to this the resistance of the two iron wires, 
each one mile in length, from A to B, and from A’ to B’, or the total of 
66.6 ohms, and we have 


569.1 + 66.6 == 635.7 

This is the true resistance of the circuit as measured from the point 
AA’ to the central exchange. 

The usual difficulty with problems of this kind is that one forgets 
to consider the line resistance, and is tempted to deal with the instruments 
as though they were in parallel, the circuit having no resistance. When 
twenty or thirty of such instruments as given in the above example are 
bridged across the line, the calculation of the total resistance becomes an 
extended problem, tedious, although not difficult. 

It will be found, however, that in such a problem on account of the 
great difference in resistance between the instruments and the line wires, 
the resulting resistance of the circuit will not be widely different from that 
calculated upon the assumption that all of the instruments are in parallel 
with wires having no resistance. However, for accurate computation, 
the line wires must be taken into account. In the above example the 






SIGNALLING EQUIPMENT 35 

difference is that of 635.7 ohms and 816.6 ohms or 180.9 ohms. This 
is an error of about 30 per cent.” 

In some cases after ringers have been in service for some length of 
time the magnets become weak. 




Fig. 48. 



Fig. 49. 


An ordinary ringer magnet should lift a weight of about 13 ounces, 
if not it should be re-magnetized. 

Another trouble which sometimes occurs is that the armature will 
stick to the core of one or the other coil. This is caused by the armature 
coming in contact with the core, as shown at “A”, Fig. 48. The manu¬ 
facturers usually drive a small brass pin into the armature or end of the 
pole piece, as shown at “B”. This prevents direct contact between the 
two, and sticking is thereby prevented. If the pin is all right and the stick¬ 
ing causes trouble, then the iron in the core has become magnetized and 
is not soft. There is no remedy for this trouble except to unwind the 
wire, and take the heads off the core, then heat it to red heat, cooling it 
slowly in the ashes of the fire, after which it can be rewound. This 
trouble is due to poor material, and ringers that have this defect should be 
returned to the factory and claim made against the manufacturers. 
Sometimes this trouble will develop in ringers of the best manufacturers, 
as it is very hard for a plant turning out hundreds of ringers per day to 
carefully inspect each one for a trouble as hard to locate as this. 

Another trouble which has happened in connection with ringers used 
in telephones where the ringer is brought in close proximity to the gene¬ 
rator, as in the type of instrument shown in Fig. 49, is that the ringer is 
sluggish, or strikes first one gong, sticking there a few strikes, and then 
striking the other and sticking. It has been found that the end of the 
ringer magnet nearest the generator, must be of the same polarity as the 
generator magnets. If the generator magnets are of an opposite polarity 
they will so affect the ringer as to neutralize the action of the ringer mag¬ 
nets, thereby causing the instrument to act in the manner above described. 
This should be remembered when placing ringers in this type phone, and 
the ringer magnets made accordingly. 

There has been a tendency of late years to use bare wire windings 
for the coils of telephone ringers. It is true that a slight gain in theoreti¬ 
cal efficiency is effected by this method, as the turns of wire are brought 
closer to the core, and their action on same is thereby increased. In 









































36 


TELEPHONOLOGY 


actual practice this gain is very slight, and is not noticeable, while it is 
entirely offset by the fact that if the ringer coil is damaged m any way, 
a new coil is necessary, as the bare wire is wound on the coil by automatic 
machinery and cannot be unwound and rewound by the hand, which is not 
the case when ordinary silk insulated wire is used. 

The bare wire windings are somewhat cheaper, and therefore among 
a certain class of manufacturers, have gained precedence. The use of 
ringers with bare wire windings should be avoided by managers who 
desire to rewind their own coils, and nothing but the best silk covered 
windings should be used. Recently wire with flexible enamel covering 
instead of silk, has been placed on the market. This appears to give 
Scitis 'actory results. 

The thickness of insulation is approximately half that of single cotton 
and two-thirds that of silk-covered magnet wire. This allows a larger 
number of turns on the same spool or same number of turns with a less 
weight of wire. The percentage of advantage of enameled wire becomes 
less in the coarser size and increases in the finer size. Enameled wire 
may be bent around a mandrel four times its own diameter without injury. 
Owing to the thinness of the insulation and its good heat conductivity, 
spools wound with enameled wire run at a lower maximum temperature 
and a lower average temperature than spools of cotton-covered wire under 
the same conditions. Enameled wire will stand a temperature of 212' 
F. without injury. 

The diameter of enameled wire is as follows: 


Size 


& S. Gauge. 

Diameter. 

24 

.022 

25 

.020 

26 

.0175 

28 

.0140 

30 

.0113 


Gauge. 

Diameter 

32 1 

.0092 

34 

.0073 

36, - 

.0062 

38 

.0052 

40 

.0042 


The most common trouble with ringers is an open coil. Before 
testing the coils on series telephones, disconnect the telephone r rom the 
line wire, then short-circuit the line posts and turn the crank. The 
bells should ring in the usual manner. If not, place an ordinary receiver 
aefoss the terminals of the bell, and leave the line posts short-circuited. 
The generator should then turn quite hard, and .the generator current 
should be heard in the receiver. If not, the trouble may be somewhere 
else in the circuit, but if the current can be clearly heard in the receiver, 
it is a pretty sure indication that one of the ringer coils is open. 

In case of bridging instruments, ; disconnect the line wires and turn 
the crank, but do not short-circuit the line posts. If the bell does not 
ring, place the receiver across the terminals of the ringer as in the case 
of the series instrument. The generator should turn hard: if not, look 
somewhere else in the circuit for the trouble. 


If the circuit is 0. K., but the bells do not ring, connect one receiver 
terminal to the left hand side of the circuit where it enters the ringer, 
then connect the other receiver terminal to the splice between the spools. 
If a sound is heard, then the trouble is in the coil between the receiver 
terminals. If no current or a very weak sound is heard, put the receiver 
terminal on the outside of the other spool, still keeping one side of 
the receiver connected to the middle point. Then if the sound of the 
generator is heard, the trouble is in the other coil. If no sound is heard 




SIGNALLING EQUIPMENT 37 

in either case put the receiver terminals across the ringer and if sound 
is heard then both of the ringer spools are open. 

Biassed and Harmonic ringers and other special types are described 
elsewhere m connection with the special equipment with which they are 
used. 

Another type of ringer sometimes used in telephone work is the 
bchwarze Bell, which requires less current than the usual battery bell, 
two ordinary dry cells will operate the smaller bells, shown in Fig 50* 
over one mile of No. 18 Copper Wire. 

When applied on High Tension Current,—for instance, on 110 volts 
—all that is necessary is a 110 volt lamp in series with the Bell, or a 
RGsistciricG Unit gqu&1 to n 110 volt lrnnp, to bring tho 3.mpGmgG down to 
the rating which is noted on the back casting of every Bell. This enables 
operation from one Central Station to large buildings without using heavy 
wire 



Fig. 50. 


To rewind Schw^arze bell coils, always when unwinding them, count 
the layers and the turns of both the primary and secondary carefully, 
and rewind them in exactly the same manner with the same size wire. 
The secondary or retarding winding is always to be short circuited. This 
arrangement is shown in Fig. 51. 




The contact springs should strike the contact points equally on each 
side, and when the armature stands neutral both points are slightly open, 
as shown in Fig. 51 at a. Adjust the gongs to the Bell Hammer in such a 









































38 


TELEPHONOLOGY 


manner that the hammer will strike both gongs with an equal blow, and 
so that the Bell Hammer will have a sufficient whip. When applying Bell 
in circuit watch the rating for operation, see that the armature swings 
free, and that the small coil which makes connections between the arma¬ 
ture and bracket is intact, and see that the brass points in the armature 
hold the armature from direct contact with the iron cores. This Bell is 
made with gongs from 21/2 to 28 inches in diameter. 

GENERATORS.—The theory of the creation of current by the mag¬ 
neto generator was discussed in the first part of this chapter and the 
design of the telephone generator at the present day is almost solely a 
question of good mechanics. The pole pieces should be made of the best 
soft iron. The center opening, or field, is accurately milled to shape, and 
the permanent magnets, which should be made of the very highest 
quality of steel are placed with their north poles in connection with one 
pole piece, and their south poles in connection with the other. 

The armature, a detailed drawing of which is shown in Fig. 52, is 

made from many punchings of soft iron, or is a special soft casting, and 
is accurately ground to fit the opening between the pole pieces as closely 
as possible. In some makes this is within one one-hundredth o" an inch. 
If possible, the steel axle upon which the armature is mounted should be 
ground to an exact fit in the brass bearings, which should be sufficiently 
long to afford a firm support for the axle. 

The gear wheels should be made from heavy cast brass with cut teeth, 
and should be so designed that they will turn smoothly and noiselessly 
without wear. 

The magnets are bent by various processes. Some bend the magnets 
cold, while some heat the magnets in the middle and make the bend, 
tempering the magnet afterwards. 

In bridging generators the greatest attention should be paid to secur¬ 
ing magnet steel of very best quality. Everything else being equal, the 
strength of the generator is proportional to the cross-section of its 
magnets. An excellent size magnet is made from ~/> x 1/2 or % inch bar. 



As the strength of the machine is proportional to the cross-section of the 
magnets, it will readily be seen that a 4 bar generator, each bar % x 1/2 
inch is more powerful than a 5 bar magnet with bars 14 x 14 inch. It is 
not a question of the number of bars, but the size, which determines the 
strength of the machine. 










39 


SIGNALLING EQUIPMENT 

"The general trade offers permanent magnet generators equipped 
with from three to eighteen bars of horse shoe type. 

These magnets vary in length, and greatly in cross-section. There¬ 
fore we find that many of the four bar magnetos are more powerful than 
some others of five bars. 

An illustration of this is shown in two types most popular to the 
telephone trade for bridging and toll line use: 

Five bars: Cross section %" X %" -f- 5 bars = 73 / s = l"/ a4 sq. in. 

Four bars: Cross section 4 / 8 " X %" X 4 bars = 96 / 8 = W 2 sq. in. 

(64 square eights = 1 inch.) 

In the above case the four bar magnet field contains 28 per cent 
greater cross-section than the five bar field. 

. We must bear in mind that our magnets are very effective, if sub¬ 
divided for the purpose of covering the whole length of the field—where 
we are limited in length and cross-section by the economy of present 
practice—and the processes applied in magnetizing them: so it is clear 
that one cannot depend on the number of bars, nor, always upon the 
cross-section of them, in selecting the best generators. One can get poor 
results from five or more small bars well magnetized, or the same number 
of large bars poorly magnetized. 

Of course, it is understood that the analysis of metals, processes of 
heating, tempering and handling of these permanent magnets during their 
manufacture enter largely into the question of good production and long 
life. In order to secure the greatest output, the permanent magnets 
should be as strong as possible, as the greater the number of lines of force 
flowing across the field, the greater will be the current. The shape of 
the poles, and the distance between them has a great deal to do with this. 
If pieces of soft iron be placed between the poles of the magnet they con¬ 
centrate the lines of force and cause them to pass across the field better 
than if they were not used, and therefore soft iron is used for the pole 
pieces. 

As the object sought is to get as many of the lines of force as possible 
to pass through the windings, the armature core is also made from softest 
iron. This causes the lines of force to pass through the wire windings 
in the manner shown in Fig. 52a. 

The importance of a small air gap, or space between the armature 
and pole pieces is at once apparent from this figure, as it will be seen that 
the greater the air gap, the more lines of force will be lost, and the greater 
the loss of power will be. Generators should therefore be selected in 
which the air gap is made as small as possible. 

The wire used in winding an armature should be of the largest size 
that will give the desired number of turns, as the voltage given depends 
directly on the number of turns of wire used. 

In series generators the amount of current required is not great, 
while the current should possess a very high voltage. 

The dimensions of an armature for a 3 bar machine are shown at “A”, 
Fig. 52, Page 38. This is wound to a resistance of 650 ohms with 3120 


*Am. Tel. Journal. 



40 


TELEPHONOLOGY 


turns of No. 36, B. & S. G. single silk covered wire. One end of the wind¬ 
ing is soldered to a pin driven in the steel axle, while the other end is 
soldered to an insulated brass pin which extends through the end of the 
armature, as shown in upper corner of Fig. 52, and is intended to make 
connection on the contact spring which is mounted on the end of the 
generator. 

A 4 bar generator armature, dimensions of which are given at “B”, 
Fig. 52, is wound to a resistance of 330 ohms, with 2640 turns of No. 33 
B. & S. G. silk covered wire, while the armature o° a five bar machine, 
the dimensions of which are shown at “C”, Fig. 52, is wound to a resistance 
of 200 ohms, with 1760 turns of No. 31 B. & S. G. silk covered wire. 

In winding generator armatures it is absolutely necessary to secure 
some form of revolution counter. The simple counter described on Page 57 
can be used for this purpose. One half the number of turns should be 
wound on one side for the armature, taking care to wind the wire evenly 
and smoothly. The wire can then be crossed over and wound on the 
other side with exactly the same number of turns. 

In some types of armatures the winding space is constructed as shown 
in Fig. 53, and the wire can be evenly wound, thus saving time and obviat- 



Fig. 53. 


ing the necessity of counting the turns on each side. An increase in effi¬ 
ciency is said to be secured, as a larger amount of wire can be wound on 
the armature. 

Before winding, the space on the armature should be carefully insula¬ 
ted with paper or cloth and shellac. Before the winding is put on a 



Fig. 54. 

string should be placed crosswise in the armature slot, the wire is wound 
over the string, and the string securely tied down to prevent the wire from 















SIGNALLING EQUIPMENT 


41 


coming loose. The entire armature should then be heavily coated with 
shellac and allowed to dry before using. 

Shellac is not absolutely the best substance that can be used for this 
purpose, but it is one of the most readily obtainable. The shellac should 
be of the best grade, and should be dissolved in 95 per cent, alcohol. Wood 
alcohol, or alcohol containing water, should not be used, as it will serious¬ 
ly impair the instrument. 

The small gear wheel on the generator armature is usually attached 
by means of a Cotter Pin or other device, which allows some lost motion. 
The object o' this is to enable the user to start the machine without a 
sudden jerk, which would happen if the gear was rigidly connected to the 
armature. This also insures smooth, noiseless running, and resulting 
uniformity in the current waves generated. The Driving Gear used by 
the Holtzer Cabot Electric Co., is shown in Fig. 54, and in detail at U. L. 
M. and F. Fig. 55. The two springs F. are placed inside piece J. and held 
in place by cap M. which is held by piece L. to armature shaft. The small 
gear wheel J, is loose on the shaft, and can only turn as ''ar as the 
elasticty of the springs will permit, owing to the small projection inside 
of M. which engages the springs. Fig. 55 shows the generator disassem¬ 
bled. 



The shunt springs H. Fig. 55, and method of operating same are the 
parts of the instrument which usually cause trouble. Several arrange¬ 
ments for series work are in common use. Two of these are shown at A 
and “B”, Fig. 56. At “A” it will be seen that the axle on the large wheel 
is normally in connection with the spring, “X”, which connects to the 
insulated pin of the generator winding; the winding is thereby snort 
circuited, which will be noted by tracing the emeu it from “P” to “F”. 



42 TELEPHONOLOGY 

at “X”. This connects the generator winding shown by the spiral dotted 
line, in circuit. 

The other type of series shunt is shown at “B” in the figure. Here it 
will be seen that the armature winding is short circuited by the long spring 
“X” coming in contact with the inner spring “Y” thus short circuiting ter¬ 
minals A and B. When the crank is turned, the axle moves inwardly, and 
in this case forces the spring “X” out of connection with the spring “Y”, 
thereby connecting the armature winding to the terminals “A” and “B”. 
It would seem that the method shown at “A” is to be preferred, as the 
axle always forms a rubbing connection on the spring, whereas in the 
method shown at “B” the connecting points simply touch and do not rub, 
and a possible cause for trouble exists. 

Several methods of arranging the springs in bridging instruments 
exist. Referring to the method as shown at “C” Fig. 56, it will be seen 
that normally the axle of the large gear wheel is out of connection with 
spring “X”, and when the crank is turned, the axle moves inwardly, thus 
connecting the generator winding to terminals “A” and “B”. 


A B c P 



The type of shunt shown at “D” can be used for series or bridging 
generators. For series lines connect to A and B and winding is short 
circuited until crank is turned- For Bridging, wires shown by dotted 
lines are disconnected from Y, lines are connected to Y and B and crank 
is arranged to move outwardly, away from X, thus making A contact on Y 
and completing the circuit. 

The armature contact as shown at “E”, Fig. 56, is often a source 
of trouble. The pin projecting from the shaft should be as large as 
possible, and the spring bearing on the pin should be long and flexible, 
so that it will not lose its tension, in which case it would fail to make 
connection. 

It is customary in the best types of generators to bend the spring 
in a “U” shape form, as shown. If the generator fails, it is best to 
examine the spring which should be held against the end of the pin while 
the crank is turned. If it is found that the spring does not make good 
connection, the trouble can sometimes be remedied by bending the spring 
so that it will properly press upon the pin. 

The usual method of rating the output of generators is to state the 
ohms resistance through which they will ring. It is about as absurd a 
method as could be imagined, as it is seldom if ever stated what the 
resistance of the bell is that the generator is supposed to ring. For 
instance: in connection with a 10,000 ohm series generator, it is not 
stated what resistance bell the generator will ring through the said 10,000 
ohms. It must be supposed on the part of the purchaser that the manu- 













































SIGNALLING EQUIPMENT 


43 


facturer means the generator will ring its own bell through 10,000 ohms. 
This is the usual acceptance of the statement. For ordinary exchange 
use a generator that will ring the bell on its instrument through a resist¬ 
ance of 10,000 ohms will prove satisfactory. 

For bridging work, the requirements are almost the reverse, and it 
is not the matter of resistance through which the generator will ring its 
own bell, but the number of bells the generator will ring. 

Some bridging generators are stated to ring through 100,000, 
200,000 or more ohms. This is of little consequence, and in purchasing 
bridging generators the fact to be considered is, how many bells will the 
generator ring on a given line. An ordinary 4 bar generator, “G”, Fig. 
57, should ring the bell “R” of 1000 ohms resistance, with the shunt “S” 
of 40 ohms resistance, through a resistance of 2000 ohms; while a 5 bar 
generator should ring the same bell through a resistance of 3000 ohms. 

Generators complying with these requirements will be found to give 
satisfaction. The bell, of course, should be carefully adjusted, and in 
testing heavy duty 5 bar instruments, it is well to decrease shunt “S” to 
36 ohms.. This may be considered equal to ringing fifty 1600 ohm bells 
through 2000 ohms resitance. 



Fig. 57. 


It is necessary in some types of generators to remove the magnets 
when repairing the instrument. When replacing the magnets they 
should be carefully placed so that the north poles are on one side and the 
south poles on the other. This is readily determined by taking the mag¬ 
nets and so arranging them that they do not stick together. If they stick 
together when the ends are touched on each other, then they are in the 
wrong position. They should be replaced in the machine with like poles 
all on one side. 

In testing generators it should be remembered that the speed at 
which the crank is turned has a great deal to do with the output. 

For testing purposes it is well to adopt a speed of 150 turns of crank 
per minute, which is about the speed the average man turns when making 
a call. 

The result from different size generators at this speed should be as 
follows or better, these measurements counting r or little, however, unless 
special instruments are used; ordinary voltmeters will not answer: 

3 bar generators 65-90 volts 150-200 milliamperes. 

4 bar generators 70-90 volts 250-300 milliamperes. 

5 bar generators 75-110 volts 325-400 milliamperes. 

A. complete generator is shown in Fig. 58. 

* Permanent magnets o' telephone generators and polarized ringers 
actually do, from various causes, lose a portion of their magnetism or in 
some cases a complete demagnetization is effected. It is needless to say 

♦American Telephone Journal. 














44 


TELE PHONOLOGY 


that manufacturers of this type of equipment have made most caiefuj 
studies of this subject, and while it is possible to use special magnet steel 
and to “age” the magnets so that under average conditions they will hold 
their magnetism practically indefinitely there is still a chance for a fuither 
loss of magnetism. For example, a generator when new will give a cer¬ 
tain output due to its strong magnets. If this generator is operated on a 
short circuit for any length of time the armature reaction will establish 
lines of force opposing those of the permanent magnets and of sufficient 
magnitude to greatly weaken them. It is easy to see that on heavily 
loaded bridging telephone lines a similar action might in time greatly 
weaken the generators. 



Fig. 58. 


Another and not uncommon way in which generator magnets are 
demagnetized is through a discharge or leakage of direct current through 
the generator armature winding. This is only possible when the genera¬ 
tors are not provided with a shunt. The permanent magnet of a polarized 
ringer is not usually affected by the passage of current through the wind¬ 
ings, as when correctly designed it occupies a neutral position in respect 
to the magnetic circuit of the coils. In addition to the losses resulting 
from the action of electric currents a partial de-magnetization of any 
magnet can result from mechanical shocks, so that even with the best 
construction it must be assumed that, when a big factor of safety in 
operation is not provided, there will be in time a necessity for re-mag¬ 
netizing. 

Polarized ringers for regular exchange work have a sufficiently large 
factor of safety, but on bridging lines where the circuits are generally 
loaded until the limit of signalling is reached there is no margin leT and 
a very slight weakening of the permanent magnets of the generators will 
immediately become known. As previously mentioned, the reaction in a 
generator under such conditions has a tendency to cause this weakening, 
so that from this point of view the practical or limiting load on a bridging 
line is reached long before the signal becomes questionable. 

The act of removing or replacing generator magnets, such as taking 
them from one generator and placing them in another, will greatly 





SIGNALLING EQUIPMENT 


45 


weaken them. In every case, they should be strongly magnetized before 
being replaced, thereby giving the generator its original large output. 

The magnetizing of new magnets or the re-magnetizing of old ones 
must be thoroughly done as there is considerable loss of magnetism 
during the process of assembling the apparatus. To prevent too great a 
loss, when the magnets are not immediately used as soon as magnetized, a 
“keeper” or armature of Norway iron is placed across the magnet poles 
until used. 



A simple and efficient magnetizing device, one which can be readily 
constructed without the use of special tools, is illustrated in the accom¬ 
panying drawings. Fig. 59 shows a cross section with dimensions, while 
Fig. 60 shows a perspective view of the magnetizer with a generator 
magnet inserted. It consists of a base of magnetic metal such as annealed 
Norway iron (cast iron -or steel will do) with a finished or plain upper 
surface. Upon this base are mounted two solenoids, made exactly alike 



Fig. 60. 


and with openings large enough to admit a generator magnet loosely, so 
that its ends will rest squarely on the sur ace of the base plate. In this 






































































































46 


TELEPHONOLOGY 


way the coils act directly on the magnet, and the only air gaps in the 
magnetic circuit are those between the ends of the magnet and the base 
plate, the latter serving as a yoke. This not only simplifies the construc¬ 
tion of the magnetizer, but gives a most efficient electrical arrangement. 

The spools can be made from any metal or thin wood, but it is prefer¬ 
able to use seamless copper tubes with sheet copper heads so as to give a 
quicker action to the coils. 



When a direct current lighting circuit of 110 or 220 volts is available 
the magnetizer should have each spool carefully filled with a winding of 
No. 32 B. & S. gauge single silk covered copper magnet wire. This wind¬ 
ing should be done in layers and the completed coils covered with book 
binders’ cloth for mechanical protection. Before winding the spools 
should be carefully insulated with heavy paper and then shellacked. A 
good paste containing no acid or other harmful ingredient should be used 
for fastening the paper insulation. (The paste known as “Photo” or 
“Photo-Library” paste will do). 

It will probably be found necessary to insert layers of paper at 
intervals during the winding so as to cover rough layers of wire and 
allow the remainder of the winding to be laid on smooth. It is not advis¬ 
able to put more than five or six layers of paper on each spool as valuable 
winding space will then be sacrificed. However, the presence of several 
papers between the layers will add to the insulation of the winding and for 
that reason is an additional advantage. The inside ends of the two 
windings should be connected together, while the outside ends are to be 
attached to the insulated binding posts provided on the base plate. The 
two windings will then be in series so as to act together. If the connec¬ 
tions are reversed the inserted magnet can be easily withdrawn when the 
current is flowing. 

If no lighting circuit is available for furnishing current for the 
magnetizers, very good results can be accomplished by using dry cells 
or other primary battery connected so as to give approximately 24 volts. 
As each dry cell when new gives one and one half volts, there should be 
at least sixteen connected in series, or if the cells are small, two or more 
sets of sixteen in series should be connected in multiple as shown in Fig. 
61. For this low voltage the magnetizer should have a winding of No. 26 
B. & S. gauge single silk covered copper magnet wire. 

In remagnetizing old magnets it is advisible to insert them in the 
solenoids in such a position as to increase the magnetism rather than to 
demagnetize them. The proper direction is readily ascertained by means 
of a small pocket compass or by suspending the magnet above the solenoid 
while the current is flowing as shown in Fig. 62. In the latter method 















SIGNALLING EQUIPMENT 


47 


the magnet will revolve so that its north pole will come 
pole of the solenoid. It should be especially noted that it 
insert the magnet in this position, so that its south pole 
north pole of the solenoid. 



Fig. 62. 




over the south 
is necessary to 
will be in the 


Fig. 63. 






















































































48 


TELEPHONOLOGY 


When using the magnetizer the magnet should be inserted in the 
solenoid before the current is connected and removed after the switch 
is open. A few seconds is sufficient time to give a good magnetization, 
the upper or projecting portion of the magnet being rocked during this 
time so as to settle its poles into better contact with the base plate. 
These magnetizing coils can be used for. re-charging ringer or receiver 
magnets by providing iron cores as shown in Fig. 63 for the solenoids. 


CHAPTER III. 


COMMERCIAL TALKING EQUIPMENT. 


As the receiver was the first piece of telephone apparatus constructed 
and yet remains one of the most important, it is advisable to consider its 
construction and repair first. Every receiver must possess three qualities. 
It must faithfully reproduce sound without distortion, and with as 
little diminution as possible, and must be so designed and constructed as 
to retain under all conditions of temperature its receiving qualities in 
spite of the rough handling to which this instrument is subjected, 
without need of re-adjustment or repairs. It should be practically 
indestructible. 

The first of these qualities can be called “Electrical Efficiency”, the 
second, “Permanency of Construction” and the third “Mechanical 
Strength”. 

In regard to electrical efficiency, it is a fact that all first class receivers 
on the market talk about the same when each one is new and properly 
adjusted. It takes an expert with delicate testing apparatus to distinguish 
between receivers of a half dozen of the leading manufacturers. In other 
words: they are all electrically efficient to a marked degree. 

Early models of the receiver were of the single pole variety, in which 
a straight magnet was used with a coil mounted upon one end. In the very 
early models the containing case was of wood. Now hard rubber or what 
is known as “Composition” shell are used. These are unaffected by tem¬ 
perature and of much higher insulating quality than wood. 

It was soon found that an increase in the efficiency of the instrument 
would be obtained by making the magnet “U” shaped, and using two 
coils. This is what is known as the Bi-polar construction, and is now 
universally adopted. 

One of the principal defects in many of the existing types is the fact 
that the adjustment of the distance between the pole pieces and the 
diaphragm varies, due to atmospheric changes, as the metal and the 
containing case expand or contract differently, thereby throwing the mag¬ 
nets nearer to or further away from the diaphragm. 

In the early types of Bi-polar instruments an attempt was made to 
remedy the unequal expansion of the metal and rubber parts of the instru¬ 
ment by attaching the metal parts to the rubber shell near the diaphragm 
by means of a threaded portion which screws into the shell. This object 
was defeated, however, on account of the use of a screw which was used 
to hold the block upon which the binding posts were mounted, in place ai: 
the rear end of the case; this screw going into the metal part of the 
receiver. This and other defects in construction caused the threads holding 

.( 49 ) 


3 




50 


TELEPHONOLOGY 


the metal parts to loosen from expansion and contraction, which made 
frequent re-adjustment necessary. 

The electrical action of the receiver is very simple, and any receiver 
when properly adjusted will give good results from the standpoint of 
speech transmission. About half the trouble met with in receivers is due 
to rough handling, for the receiver is tampered with more than any other 
part of the telephone. It is generally the first part attacked when the 
instrument fails to give satisfaction, and therefore in some models, this 
trouble is obviated by securely locking the case in such a manner that 
the receiver cannot be opened except by the use of a special wrench or 
other device. 

The diaphragm plays an important part in the operation of the 
receiver, and the structure supporting it in front of the pole pieces should 
be carefully constructed. There is a growing tendency to use a metal cup 
for this purpose upon which the diaphragm is placed and held by a metal 
cap, which secures it in position irrespective of the outer receiver case. 

The diaphragm should be carefully cut so that it is absolutely flat 
and so that the edge is not turned up or dished. 

Diaphragms in commercial use are made from two materials: ferro¬ 
type sheet, which is common sheet iron coated with Japan, or sheet tin, 
which is sheet iron coated with tin. The ferrotype diaphragm gives very 
good results in connection with receivers adjusted to work with it, while 
in other cases the tin diaphragms give the best results. 

When a receiver is purchased with a ferrotype diaphragm it is bad 
practice to substitute a tin diaphragm, and, of course, when the instrument 
is adjusted for use with a tin diaphragm do not substitute a ferrotype. 

For the pole pieces the softest iron should be used, and the pole 
pieces should be permanently attached to the magnets, the greatest possible 
surface being secured. This is accomplished in most makes by carefully 
milling the ends of the magnets and pole pieces and then forcing them 
together under pressure, finally binding the entire structure together 
by means of a heavy bolt. If the receiver is ever taken apart, always make 
sure when putting it together to get this bolt tight. 

Most receiver coils are wound directly on the soft iron pole pieces, 
rhe spool heads being usually made of brass. The wire is prevented from 
coming in contact with the heads by means oi fiber washers, while the 
space between the heads is covered with paper. In one modern type of 
receiver, the wire is wound on spools made from small stampings, 
which are slipped over the heads of the pole pieces and held in place by 
screws. This affords an easy means of removing and rewinding the spools 
when necessary. 

The magnets should be constructed from steel that will permanently 
retain its magnetism for an indifinite period. 

The claim made by some of the smaller manufacturers regarding the 
weights their receiver magnets will lift are amusing, as the lifting power 
of a receiver magnet has very little to do with the efficiency of the instru¬ 
ment. In fact, a very strong magnet is not advisable. In proo' of this it 
is a well known fact that the old single pole receiver has seldom, if ever, 
been excelled for clearness of articulation, the modern double pole instru¬ 
ment with its stronger magnet, being louder but not clearer. 

The thickness of the diaphragm has a great deal to do with the various 
qualities of the transmitted speech, such as clearness and volume. 


COMMERCIAL TALKING EQUIPMENT 


51 


Probably the accoustic properties of the diaphragm hav« received less 
attention than any of the other properties of the receiver. When the re¬ 
ceiver diaphragm is acted on by the magnetic force, its tendency is to 
vibrate as a whole, emitting a certain note called its “fundamental" and 
others called “over tones.” These mingle, and the resultant sound is an 
exact duplicate of the original one, the different shades and tones being 
faithfully reproduced. 

With a thin diaphragm, clearness is gained at the expense of volume, 
while with a thick diaphragm louder transmission is obtained, and the dis¬ 
tinctive over-tones and sharpness is sacrificed. A thin diaphragm makes 
the voice appear to be shrill and high pitched, while thick diaphragms 
give the voice a heavy, growling tone. 

The adjustment of the diapragm and pole pieces is an important de¬ 
tail. This is accomplished in various ways, the usual one being that after 
the instrument is assembled, the face of the cup and upper ends of the pole 
pieces ai e ground, the pole pieces being ground slightly lower than the rim 
of the cup. The difference is the “adjustment” of the instrument. In 
modern types, no attention is paid to means for re-adjusting the instrument, 
as in properly constructed receivers there is no need of re-adjustment. 

Modern receivers are so constructed that an ordinary cord with tips 
on both ends can be used, and receivers requiring special cords should be 
avoided, for, if it becomes necessary to buy cords for re-equipment, they 
must be purchased from the same factory, who having a monopoly of the 
business, can maintain any price they please. 

The concealed cord receiver is now in general use, and the instrument 
with binding posts on the outside while in general use, does not seem to 
meet with as much ^avor as the concealed type, the latter model not requir 
ing as frequent cord renewals. 



Fig. 64. 


There are three points of importance to be considered in a receiver 
where low cost of maintainance is desired. 

First: The shell should not support the working parts, but should 
simply serve to insulate the metal parts, and act as a casing only. 

Second: The receiver parts should be held in position in such a manner 
that if the outer case becomes broken the instrument will still be operative. 

Third: Every part should be easily accessible and readily interchange- 





52 


TELEPHONOLOGY 


able in case of damage, and should be manufactured of such mateiial 
as will stand mechanical shocks so that a relative change of position is 
impossible. 

One type of instrument fulfilling these requirements, which can be 
taken as representing the present state of receiver development is shown 
in Fig. 64. The coils and pole pieces are inclosed in a case of heavy metal. 
Upon the top of this metal cup threads are cut, and when the diaphragm 
is in place the metal ear piece corresponding to the ordinary receiver cap 
is securely screwed in place upon the metal cup. This incloses every work¬ 
ing part of the receiver, including the diaphragm, in a metal case, which 
prevents the diaphragm from being injured in case of a broken shell. 
In fact the instrument will operate just as well without the outer shell. 

The metal cap can if necessary be locked in place by a Spanner wrench 
which prevents the curious from tampering with the instrument, as it is 
impossible to remove the metal cap without the wrench. As the inner 
metal cup completely incloses the diaphragm except at the centre opening, 
the receiver can be placed firmly against the ear in case the outer cap is 
missing without affecting the vibrations of the diaphragm. 



Fig. 65. Fig. 66. 


The coils of the instrument are wound in such a manner that the 
adjustment and assembly of the receiver is complete before the coils are 
put in place. In the first model of this instrument the coils are wound on 
spools which are slipped on the head of the pole pieces and are held in place 
by means of screws, as shown in Fig. 65. If it should become necessary 
to replace the coils, it is only necessary to take out the screw and slip the 
coil off the pole piece. In some receivers the coils may be replaced by 
taking out the bolt holding the pole pieces and magnet in place. This 
allows the pole pieces to be taken out and the coils rewound, and this 
method is used in the last model of the above instrument. 

Cord terminals in receivers are usually located between the sides of 
the magnet, and should be made of brass or some other metal. The screws 
for holding the cord tips should go into brass sockets or terminals. 

The terminals should be so constructed that either loop or tip cords 
can be used, and should be connected to the receiver coils by means of 
heavy strips of brass or other metal insulated by hard rubber. The fine 
wires from the coils should not run the cord terminals, as the wire is 
easily broken. 

In some instruments the receiver diaphragm is held in place by a ring 
exactly the same as the brass cap heretofore mentioned, except that it does 
not extend over and completely cover the diaphragm except at the centre 
opening. This method of clamping the diaphragm firmly in place irre- 







COMMERCIAL TALKING EQUIPMENT 


53 


spective of the outer shell is rapidly coming: into use and would seem to 
represent the best practice. As shown in Fig. 66 the loosening of the cap 
or falling apart of the shell cannot in any way affect the instrument. The 
diaphragm cannot change its position or come in contact with the pole 
pieces as all parts of the receiver are forced together under heavy pressure 
in addition to being bolted. The wires connecting the coils to the binding 
posts cannot break off, as flat strips of brass are used, which are incased 
in hard rubber insulation thereby preventing short circuits. 

The lodgment of dirt in the receiver, especially metal particles, is 
prevented owing to the brass containing case being almost air tight. 

The standard Bi-polar receiver used by the Bell Company is shown in 
Fig. 67. The case is in three pieces, the body, tail piece upon which the 
binding posts are mounted, and the cap. 

The magnets are made from steel bars 3 1/2 inches long, .63 in. wide 
and .26 in. thick. At the rear end these are bolted together with an iron 
bolt and iron filling: piece, and thus form a U shaped magnet. To give 
the instrument sufficient weight a piece of lead is secured between the 
magnet bars. 

The end carrying the binding posts is fastened to the iron filling 
piece by means of a screw. A screw eye is provided to which the tie 
string on the receiver cord should always be fastened so as to take the 
strain from the cord conections. 



Fig. 67. 


The binding posts are connected to the two spool windings, which are 
wound in opposite directions and connected in series. Bolted between 
the ends of the U shaped magnet and the pole pieces is a brass block, 
threaded to engage a thread on the inside of the shell. The adjustment 
is accomplished by turning the entire magnet structure in the shell until 
the tops of the pole pieces are a sufficient distance below the edge of the 
shell. A pin is then driven downwards through the edge of the brass 
piece and into the body of the shell, thus securely locking the adjustment 
in place. The adjustment is unaffected by temperature changes or in fact 
any thing except the actual breaking of the shell. 

Fig. 68 shows the concealed terminal receiver used by the Bell Com¬ 
panies. The construction is self evident. In this type the lead block is 













54 TELEPHONOLOGY 

omitted, the receiver being sufficiently heavy to actuate any standard 
switch hook. 

The receiver shown in Fig. 68 is typical of several instruments now 
on the market. It is a very efficient instrument and represents the latest 
model of receiver equipment with the exception of the instruments wherein 
the diaphragm is secured in place by a metal cap which type would seem 
to possess the advantage of greater mechanical strength. 

The adjustment of the modern receiver is usually determined at the 
factory, and if properly constructed the instrument seldom if ever needs 
re-adjusting. The average adjustment given magneto receivers is about 
eleven thousandths of an inch when tin diaphragms are used. This varies 
to about fourteen thousandths of an inch with ferrotype diaphragms. 



Fig. 68. 


If through any cause it becomes necessary to increase the distance 
between the diaphragm and pole pieces a careful fileing will accomplish the 
desired result. Great care should be taken to remove all metal particles 
from the receiver before replacing the diaphragm. 

A diaphragm which is bent or dented should never be used, as dia¬ 
phragms cannot be straightened if once bent, but a new one should be 
provided. 

Always remove the rust from a diaphragm before putting same in 
place. Screw the cap on hard as the diaphragm must be tightly clamped 
to give the best results. 



Fig. 70. 































































COMMERCIAL TALKING EQUIPMENT 


55 


i 

A good rough method of making receiver tests is shown in Fig. 69. 
Here the receivers to be tested, “A” and “B”, are connected to a double 
pole double throw knife switch, as shown. Wires are run to the line 
posts of an ordinary telephone, and in series with one wire is connected a 
resistance box, “X”. The speaker at the telephone talks or counts in an 
ordinary tone of voice, while the party at the receiver listens, first to 
receiver “A” and then to receiver “B”, meanwhile throwing the double 
pole switch. 

Resistances can be inserted in the circuit by means of the resistance 
box, and the amount of resistance through which the instruments can 
be heard will determine their relative efficiency. 

Receivers, transmitters and other telephone equipment cannot be as 
accurately tested as other electrical devices, as there are no standards of 
comparison. 

A very good method when the means are at hand for testing receivers 
is shown in Fig. 70. In front of an ordinary phonograph, is suspended 
the transmitter “F” connected to a telephone. The receivers under test 
are connected to the other end of the line, and comparisons are made by 



Fig. 71. 


W 




" L *‘ 

A 


o 




V 

LLJ.1 




Fig. 71a. 


listening to the phonograph. By means of the double pole switch arrange¬ 
ment two or more receivers can be compared. For this purpose it is best 
to place a speaking record on the phonograph and to repeat the same sen¬ 
tence as each receiver is tried. This method at least enables the same 
set o ’ words to be used in the same tone, each time. By adding resistance, 
the comparative efficiency of the receivers can be determined, for, if one 
receiver can be heard through 100,000 ohms while another can only be 
heard through 50,000 ohms, the first one is twice as good as the last, pro¬ 
vided the articulation is as good. 

Where it is desired to test transmitters the positions can be reversed, 
and a standard receiver can be used at the listening end of the line while 
various transmitters can be placed in front of the phonograph, the listener 
finally picking out the transmitter which gives the best results. More 
complete information regarding transmitter testing is given in another 
chapter. 

A few troubles in the adjustment and winding of receivers may be 
met with which are easily remedied, but it is better to return the receivers 
to the factory when the trouble is in the adjustment or other mechanical 
disarrangement. 

A gauge Fig. 71, showing the exact adjustment of a good receiver of 
a certain make, should be made by taking a bar of metal and fileing same 
so that ’the ends will rest on the sides of the receiver case and the centre 
































56 


TELEPHONOLOGY 


will just touch the pole pieces. Make this carefully. The receivers of the 
same make under test for adjustment can then be measured by this guage, 
and if any of them are found out of adjustment, they can be readjusted or 
returned to the factory. 

Coil troubles are readily determined by disconnecting the receiver 
from the telephone and tapping the ends of the cord on a battery. If no 
click is heard, the coils are probably open and should be rewound. Test 
the cord carefully and see that it is 0. K. before making this test. 

It is easy to determine which coil is open by using another receiver 
as shown in Fig. 72. By holding one terminal of the testing receiver on 
the splice between the coils of the receiver under test, the open spool in 
the damaged receiver can easily be determined. 

The dimensions of a standard receiver spool are given in Fig. 71a. 



Fig. 72. 


For local battery or magneto work each spool is wound with 605 
turns of No. 38 silk wire, resistance 50 ohms per spool, or 100 ohms to the 
pair. 

In winding the spools particular attention should be given to have 
each spool wound in the same direction and then join the two inside termi¬ 
nals together, the outside terminals going to the binding posts of the 
receiver. This accomplishes the same result as if the coils were wound 
in opposite directions and connected in series. 

A receiver for common battery work has each spool wound with 380 
turns of No. 34 single silk wire, each coil measures 121/2 ohms. The two 
inside ends of the coil are connected together, the outside ends go to the 
receiver binding posts. The total resistance of the two coils is 25 ohms. 
The receiver is used with closed secondary coils. 

A standard common battery receiver has each spool wound with 661 
turns of No. 35 silk wire, each spool having a resistance of 30 ohms. The 
spools are connected in series, as previously described. This is the instru¬ 
ment commonly used with condenser circuit common battery telephones. 



Fig. 73. 


Another receiver for common battery work has each spool wound with 
580 turns of No. 35 silk wire. This gives each spool a resistance of 50 
ohms. The two inside ends of the spools connect together and go to one 







COMMERCIAL TALKING EQUIPMENT 57 

Binding Post and the two outside ends connect together and go to other 
Post. 

Two methods of holding receiver spools that are to be wound are 
shown in Figs. 73 and 74. The wire should be as evenly wound as 
possible. Before winding, the core of the coil should be carefully insula¬ 
ted with one or two layers of paper. The wire should be prevented from 
coming in contact with the heads by paper or fibre washers. 

To secure an accurate balance the number of turns on each spool 
should be the same, and it will be found that if the same number of turns 
on each spool is obtained, the resistance will be the same for each spool. 



The spools can be wound nearly full : then a layer of paper should be 
put on the spool, and the last layer of wire can be easily and smoothly 
wound which gives the spool a finished appearance. The outside terminal 
wires should be doubled and brought out and soldered to the terminals. 

Before winding the spool, a heavy wire should be soldered to the wire 
with which the spool is wound, and one or two turns of this wire should 
be wrapped on the spool, the splice carefully insulated by wrapping with 
paper, and the regular winding process begun. This prevents the fine 
wire from being broken. 

A good revolution counter for winding receivers and other coils is 
shown in Fig. 75. This is an inexpensive device and is indispensible 
where accurate winding is to be done. 



Fig. 75. Fig. 76. 


A simple revolution counter can be made from a clock of the usual 
“alarm” variety, by removing the escape wheel and soldering to the axle 











58 


TELEPHONOLOGY 


of the minute wheel a piece of flexible shaft made by wrapping some steel 
wire in a tight spiral. Attach the end of this shaft to the winding machine 
and upon turning same, the hands of the clock will be found to move. By 
marking the distance over the dial that the minute hand moves for each 
10 revolutions of the machine a reliable revolution counter can be made 
which can be instantly set back to zero by turning the setting button in 
the usual manner. It will be found that about 480 turns per hour is what 
the average clock will indicate, that is, when the minute hand moves once 
around the dial, it represents 480 turns. 



Fig. 76 shows the usual form of head receiver used for switchboard 
work. The magnets are formed from round punchings from flat stock, 
while the pole pieces are formed from soft iron same as in the hand 
receiver. In construction and operation this instrument is identical with 
the hand receiver previously described. 

*To those of our readers experimentally inclined, or those desiring to 
audibly witness the passage of an electric current through a conductor 
without the usual concomitants of a magnet and diaphragm, which is, 
as far as the knowledge of the writers extends, the only known means of 
hearing the flowing current; the following experiments will doubtless be 
of interest. 

Some years ago while experimenting along other lines one of the 
writers devised a plan, Fig. 77 to demonstrate and compare the expansion 
of metals due to the heat of the electric current passing through the same. 

Referring to Fig. 77, A represents a base provided with an arm B, to 
which is attached at fulcrum F, a long lever or pointer C, capable of moving 
in the fulcrum F in a vertical arc, the long or arrow end traversing the 
degrees D, which are merely empirical but spaced about sixteen to the 
inch. 



Fig. 78. 


To the short end of the pointer at G is attached two wires, E and H, 
the former being the wire under investigation and the latter wire intended 


‘Am, Tel. Journal. 










































COMMERCIAL TALKING EQUIPMENT 


59 


to conduct the current from the source of power K to one end of the experi¬ 
mental wire E; the other end of wire E is attached to the screw eye J, and 
by means of the screw eye may be adjusted until the pointer registers with 
the topmost degree. Also attached to J is a wire I, leading to the opposite 
pole of the source of energy. Under these circumstances it was found that 
with small wires E such as, say No. 30 copper, the expansion of the wire 
with even a single cell of carbon battery was most marked indeed, regis¬ 
tering for copper several degrees, each time the circuit was completed 
and retiring to zero whenever it was opened. With other metals in place 
of wire E, different expansions were noticeable and an interesting and 
instructive comparison on the expansibility of various metals was made 
possible. 

Some time since, this old experiment was in some manner brought 
back to the attention of the writers when it occurred to them that there 
were other and possibly more useful or commercial possibilities along the 
same lines; accordingly the following arrangement was devised, Fig. 78. 

A is the shell of a telephone receiver, B is the usual cap, C the 
diaphragm and attached thereto electrically and securely, at point G, is a 
wire H, the other end being similarly connected to binding post F at point 
E; the binding post being so arranged that tension can be applied to the 
wire H and through it to the diaphragm C. At D is connected a wire to 
the diaphragm and another wire is connected to the binding post as 
shown. Now these two conducting wires are attached to a source of cur¬ 
rent, the diaphragm C and the wire H form a portion of the conducting 
path, and the passage of the current through this circuit is not only plainly 



audible whenever the circuit is made or broken but more surprising still 
it actually approximates in sensitiveness the ordinary telephone receiver 
and most surprising of all, it will receive and produce speech. Our first 
effort to use it as an ordinary receiver was with a central energy system 
of that type in which the receiver is placed directly in the path of the cur¬ 
rent. In view of our previous experiments and the conclusion that we 
had already naturally reached, namely, that we were dealing simply with 
the expansion and contraction of a metal due to heat, the alternate elong¬ 
ations and retractions of the wire H being communicated we were scarcely 
prepared to credit our ears when we later discovered that a condenser 
might he inserted in the circuit without excessively modifying the results. 
We then continued our investigation as follows, fiom the results of which 
we are now inclined to believe that molecular movement of some sort 
rather than heat is the basis of the action. We reasoned that if five inches 
of wire produced a certain loudness of sound, ten inches would produce 
more, because the amplitude of the diaphragm movement would be 
increased by the greater expansion of that length of wire. This did not 
prove to be the case, but as the apparatus at hard did not admit of anchor¬ 
ing the end of the wire at the back end of the shell, we concluded that that 
fact was the cause of the failure. We then tried a coiled wire of German 
silver reasoning that that would be the equivalent of a longer wire. With 
this arrangement the results were mediocre and about that time wc discov- 





60 


TELEPHONOLOGY 


ered much to our astonishment that it was wholly unnecessary to anchor 
the back end of the wire or to have either it or the diaphragm under stress 
as we at first supposed. These discoveries directed out attention to the 
molecular hypothesis and we accordingly tried the following: Discarding 
the wire H we substituted for the same a wire wound around the dia¬ 
phragm as per Fig. 79, making it a part of the circuit. 

With this plan we reproduced all the results of the previous methods 
which seemed to point most strongly to the molecular movement theory. 
The addition of more convolutions or the use of only a single wire drawn 
across the top of the diaphragm appeared to make an appreciable change, 
but with an additional diaphragm placed over the top of the other the 
loudness was increased. 

Our experiments were limited to copper and German silver wire and 
to light iron diaphragms and we have often thought it would be interest¬ 
ing and possibly useful to follow up the line of investigation, but our time 
and attention being engrossed in other directions, we have been unable 
thus far to do so. It is possible a receiver practically devoid of self-induc¬ 
tion and resistance might be devised and it is perhaps not beyond the 
bounds of possibility to produce a receiver more sensitive than the common 
permanent magnet type. What bearing would this receiver have had upon 
the telephone patents in 1876? 



Fig. 81—82. 


TRANSMITTERS.—The next important part to be considered is the 
Transmitter. An early type extensively used, is shown in Fig. 81. 

The Diaphragm H is a thin disc of Carbon, and also forms the front 
electrode. Supported behind this is the carbon block electrode C. Be¬ 
tween C and H is placed a quantity of small carbon balls known as 
“Globular” carbon. These are held in place by the felt ring B. 

This instrument in various types was extensively used, and gives 
remarkably good results, as the transmission is not only clear and distinct, 

but is entirely free from metallic sounds. 

_ \ 

The chief objection to this type is the easily broken carbon diaphragm 
which also absorbs moisture from the breath. This penetrates to the 
globular carbon causing same to “pack” or adhere together, making 
the instrument inoperative. 

When repairing this type, no adjustments are required, it only being 
necessary to replace the diaphragm if broken, and see that the proper 



















COMMERCIAL TALLINK EQUIPMENT 


61 


amount of globular carbon is used. Do not fill the chamber full, three 
fourths full is the proper quantity; and see that the felt ring is in proper 
position to keep the carbon from falling out. 

It is advisable to coat the front of the carbon diaphragm with some 
moisture resisting compound such as lamp black mixed with shellac. 

The circuit through this transmitter is from the frame supporting 
the diaphragm across the globular carbon to back electrode C, which is 
mounted on an insulated support. 

While this is an excellent Local Battery Transmitter, it is not suita¬ 
ble for Common Battery. It is a low resistance transmitter, and passes 
more current than modern types, thus necessitating frequent battery 
renewals. 

A rear view of the complete instrument is shown in Fig. 82. 

The transmitter now in common use is the so-called “solid back” 
type which has replaced all earlier models. A sectional view of the 
“solid back” as used by the Bell Company is shown in Fig. 83. 



The diaphragm h, 214 in. diameter is made of aluminum .021 in. 
thick, and is painted on the outside to prevent corrosion. The dia¬ 
phragm is attached to the carbon electrode i by means of the brass stem 
g. The electrode i is insulated from the other parts of the transmitter 
frame by means of the mica diaphragm e about .0015 in. thick, which 
is clamped in position by means of the ring b. .0005 in. variation in 
thickness of the mica will cause a variation in the efficiency of the instru¬ 
ment. Granular carbon of uniform size is placed between electrodes i and 
c and when the transmitter is spoken into, the varying pressure of elec¬ 
trode i against the mass of granular carbon between it and electrode c 
causes a variation of the current. 

No. 40 granular carbon is usually used for local battery transmitters, 
No. 60 or 80 being used or Common Battery work. The Bell companies 
use the common battery or high resistance transmitter for both common 
and local battery telephones, and when 3 cells of battery are used (for 
local battery) the results are very satisfactory and a saving in battery 
maintainence is claimed. 

The distance between the electrodes in this type of transmitter is 
about 1-16 inch, and this distance determine.-, to some extent the resist- 





















62 


TELEPHONOLOGY 


ance and efficiency of the instrument. It is highly important that the two 
adjacent surfaces of the electrodes should be absolutely parallel and that 
they should be highly polished. This can be accomplished by rubbing 
them on a lapping plate (a smooth piece of iron with fine grooves across 
it) or piece of smooth slate, using some dry red lead and finishing on a 
smooth soft cloth. When assembling a transmitter the fingers should 
never touch the surface of the electrodes, and the carbon should be abso¬ 
lutely dry, clean, and of uniform size. The separation of the electrodes 
should be such that at least three of the carbon granules used if in a 
straight line, will have room to lie between the surfaces. 

In refilling the chamber with carbon, care should be taken to use the 
same size and grade of granules as originally used. Do not fill the 
chamber too full, leave a space at top of chamber, as shown in Fig. 84. 

Fill the chamber, then tap gently on bottom to shake carbon down. 
Don’t expose top of button but always leave space at top as shown. 

The current for operating this transmitter should not be less than 
.14 of an ampere (measured at the terminals of the transmitter), nor 
should it at any time exceed .32 ampere. 



Fig. 85. 


Fig. 85 shows a complete “Bell” transmitter with a section cut away 
to show the different parts. 

The frame or case of this transmitter is connected to one side of the 
circuit, which, for some classes of work is objectionable. To obviate 
this the transmitter shown in Fig. 85a was devised. The arrangement of 
the various parts is practically the same as in the standard Bell transmit¬ 
ter, except the cell is mounted on a stamped back, as shown. This back, 
carries two insulated lugs to which the circuit wires are connected. The 


COMMERCIAL TALKING EQUIPMENT 


63 


frame is not connected to the circuit, because the rubber band around the 
diaphragm also encloses the edge of the metal cup carrying the cell. 
The cell cup and diaphragm are held in the frame by the two felt tipped 
dampening springs. 

The dampening springs are used in the majority of transmitters to 
limit undue vibrations of the diaphragm, which often cause annoying 
“side tone.” In other words the instrument is too responsive to slight 
noises. 

The average resistance of transmitters varies from a few Ohms to 
100 or more, depending upon the carbon used, etc., transmitters for com¬ 
mon battery being of higher resistance than those for local battery. 

The Bell transmitter as previously described is the result of many 
years of experience and is undoubtedly a very satisfactory instrument, 
it’s clearness of articulation being particularly noticeable. The circuit 
through this transmitter is from the brass bridge carrying the stem a, 



Fig. 85a. 


Fig. 83, which is connected to the back electrode, through the granules to 
the other electrode connected to the brass piece g. Most of the instru¬ 
ments now manufactured, resemble this instrument to a marked degiee, 
and to describe one is to describe them all except in detail, many manufac¬ 
turers having improved upon the original instrument. 

Many transmitters patterned after this instrument are open to the 
objection that in time they will pack, the carbon having a tendency to 
settle to the bottom of the cell where it forms a solid mass, thus short 
circuiting the instrument. Another objection would seem to be the 
fact that the diaphragm carries the weight of the brass piece and trout 


64 


TELEPHONOLOGY 


electrode, and that in addition to this, the motion of the diaphragm is 
restrained somewhat by the mica diaphragm. The nuts which secure the 
front electrode to the diaphragm are another source of annoyance, as these 
cannot be painted and consequently may corrode after the transmitter 
has been in use some time. It is necessary to remove the nuts when dis¬ 
assembling the transmitter, and the mica diaphragm is often broken when 
doing this. 

The Western Electric Co., who make the Bell transmitters, claim 
to use carbon prepared from coal, especially fine and hard, obtained from 
a special vein. Their instruments are certainly free from any tendency 
to “pack” and are very uniform in quality, thus showing good workman¬ 
ship and careful inspection. 



Fig. 86. 

As the different Bell companies invariably return all transmitters 
requiring repairs to the factory, several features which would tend to 
make their instruments easy to repair, have apparently been passed over, 
the aim evidently having been to produce an efficient instrument of per¬ 
manent construction. 

The transmitter manuactured by the Kellogg Switchboard and Supply 
Co. represents a departure from the type previously described. A sec¬ 
tional view of this instrument is shown in Fig. 86. 

The cell C. is stamped in and forms part of the diaphragm D. In the 
cell is secured the front electrode F. 

The rear electrode R is mounted on a stem and supported in the cen¬ 
tre of a mica diaphragm A, the mica being fastened to the main diaphragm 




















COMMERCIAL TALKING EQUIPMENT 


65 


by a small ring and rivets as shown, thus closing the cell, in which granu¬ 
lar carbon is placed. The rear electrode R is held rigidly by the stem 
which is secured to the back bridge. 

Referring to the figure it will be seen that the entire cell containing 
the front electrode and granules is vibrated when the instrument is spoken 
into, this causing the granular carbon and the front electrode to approach 
and recede from the back electrode. This action is different from the 
Bell instrument, where the motion is a piston effect produced on the gran¬ 
ules which are stationary, by the front or movable electrode only, the 
back electrode being stationary. 

In the Bell transmitter there is: 

One stationary cell, one stationary electrode, one movable electrode, 
a mass of granular carbon subject to compression between the two elec¬ 
trodes. 

In the Kellogg: 

One movable cell, one stationary electrode, one movable electrode, 
a mass of granular carbon moving with the moving electrode and subject 
to compression between the electrodes. 

Owing to the entire cell being in motion the instrument does not pack 
and a very efficient instrument is produced which is particularly economi¬ 
cal in battery consumption. 

By providing an insulated terminal for the wire coming from the 
diaphragm which forms one side of the circuit, and insulating the stem 
of the back electrode from the bridge, the shell of the transmitter forms 
no part of the circuit. 

This transmitter represents a radical departure from early models, 
which were usually variations of the White “solid back” or Bell transmit¬ 
ter. 



The next type to be considered is represented by the Dean Elect. Go’s 
instrument shown in Fig. 87 which is indeed a radical departure fi om 
former models. 

The figure plainly shows the arrangement of the various parts, which 

should now be familiar to the reader. 

The main aluminum diaphragm is formed with a hole in the centre, 
having an annular flange turned inwardly. This engages the aluminum 
electrode cup which has a metal electrode secured in the front and a carbon 
electrode mounted on a mica diaphragm in the back. The action of this 
















66 


TELEPHONOLOGY 


instrument is similar to the Kellogg instrument, as the front electrode, 
cell, and mass of granules move, while the rear electrode is stationary. 

While the cell is in contact with the main diaphragm, it does not form 
part of same, therefore the diaphragm may be removed and a new one 
substituted without changing the cell. 

Owing to the diaphragm being stiffened by the annular ring or flange 
around the centre opening, no dampening springs are necessary in contact 
with the diaphragm. 

Owing to the initial outward tension given the diaphgram, if the cir¬ 
cuit is kept closed and the transmitter is left at rest—such as when a re¬ 
ceiver is accidentally left off the hook—the heating effect of the current 
flowing causes the diaphgram to expand outwardly, thereby increasing 
the distance between the electrodes and causing the resistance to increase 
to a considerable extent. A saving in battery consumption is thereby 
affected. 

The edge of the diaphragm is turned outwards and rests against a 
ring of oiled cloth, thus doing away with the often troublesome rubber 
band. 



Fig. 88. 


The main diaphragm in this and several other makes of transmitters, 
is protected by a disc of thin moisture proof substance such as celluloid or 
oiled silk, which takes the place of the black enamel used in the Bell and 
other transmitters. 

The use of a fine wire connection between the front electrode and the 
terminal is eliminated in a very clever manner. The back electrode stem 
is mounted on an insulated block; this forms one side of the circuit. The 
front electrode is connected to the circuit through a light spring which 
rests on the rear ring holding the mica diaphragm in place, this spring 
being connected to an insulated terminal mounted on the bridge. 

This transmitter represents a very unique and simple form of con¬ 
struction, the mechanical design presenting several features which make 
it distinctive as a type and typical of modern practice. 

A peculiar form of construction is shown in Fig. 88 which shows the 
transmitter manufactured by the Interstate Elect. Mfg. Co. 

The cell is cast in the front. A stationary electrode is mounted in the 
bottom of the cell as shown. The other electrode is mounted on a mica disc 
as usual, and occupies the position as shown in the Figure. 


COMMERCIAL TALKING EQUIPMENT 


67 


Suitable openings around the cell permit the sound vibrations to reach 
the diaphragm which is attached to the insulated electrode. 

The circuit of this instrument is from the shell or case, through the 
granular carbon to the electrode attached to the diaphragm. A suitable 
connection leads from the diaphragm to an insulated terminal located on 
a projecting lug formed on one side of the front. 

The method of attaching the mouth piece is entirely different from 
other makes. The mouth piece screws on a projection formed on the front. 
The holes in the mouth coincide with those in the front thus permitting 
free access for the sound waves. 

This form of construction permits of assembling the instrument with¬ 
out the use of a bridge. It would seem very difficult to insulate the work¬ 
ing parts of this model from the case, owing to the front electrode being 
mounted on the case itself. 

The operation of this instrument is most peculiar. It would seem 
to work oppositely from any other, as the sound vibrations first lessen the 
pressure on the granules. The increase in pressure and consequent lower¬ 
ing in the resistance of the instrument only taking place when the dia¬ 
phragm springs back past the neutral point after receiving an impulse 
from the sound waves. 

The presence of the granule chamber directly in the mouthpiece 
opening does not seem to affect the transmission. The fact that the con¬ 
nection between the diaphragm and the electrode is open to the corrosive 
action of the breath would seem to be an objection to this type, although 
no trouble from this source has been reported. 

The usual dampening springs, not shown in the cut, are used to elimi¬ 
nate over sensitiveness. 

A radical departure from the types previously described is the use of 
two diaphragms. An instrument embodying this feature is shown in Fig 
88a. 



Fig. 88a. Fig. 88b. 


The diaphragms C and D are connected to the electrodes E and F, 
these electrodes being insulated from the containing cell by means of mica 
diaphragms. Granular carbon is placed between the electrodes, and the 
two diaphragms and cell structure are’supported by a suitable mounting. 

The mounting is enclosed by a case A, so shaped that the sound waves 
are equally distributed to the diaphragms. 

The current passes from one diaphragm and electrode through the 
granular carbon to the other electrode in the usual manner, the circuit 
wire being marked 1 and 2 in the figure. 





















































68 


TELEPHONOLOGY 


This model represents an attempt to secure a greater extent of move¬ 
ment between the two electrodes, and consequently a greater variation in 
the resistance of the circuit. As the instrument is of comparatively 
recent invention, no very accurate data as to its efficiency as compared with 
single diaphragm types is at hand. 

There are quite a few models of the double diaphragm construction. 
The one shown in Fig. 88a is representative of the type, none of which 
have come into extended use. 

The construction of the transmitters described thus far is such that 
only a variation in the amount of a current flowing in one direction is 
accomplished. 

Fig. 886 shows an instrument designed to convert the vibrations of 
the diaphragm into alternating impulses. 

The arrangement of the electrodes is such that their operation is 
similar to a pole changing switch. Four resistance cells containing granu¬ 
lar carbon are used, these cells being arranged in pairs. The vibration 
of the diaphragm increases the pressure in one pair of cells, and decreases 
the pressure in the other pair. The current is thereby switched in alter¬ 
nately opposite directions through the induction coil. 

Referring to the figure, G is the stationary electrode provided with 
carbon faces. The end stationary electrodes are shown at K and J. Be¬ 
tween these the movable electrodes M and N are placed. These are con¬ 
nected to a stem connected to and moving with the diaphragm. 

The movable electrodes are connected with the battery, and the fixed 
electrodes with the coil circuit, as shown on the right of the figure at A 
and B. 

The operation of the device will be understood by reference to A and 
B. When the movable electrodes are impelled to the le f t the resistance to 
the passage of a current between the electrodes N and G and M and K is 
diminished, while it is increased as between electrodes N and J and M and 
G. Consequently the greater part of the battery current will pass over the 
wire T, the movable electrode N, the stationary electrode G upward through 
the wire connection V, thence through the wire connection U to the station¬ 
ary electrode K, and thence through the movable electrode M and wire T 
to the battery. 

An impulse to the right as shown at B reverses conditions, producing 
a downward current through the wire V the changes from the one condition 
to the other being gradual and without sensible interruption, the result 
being that the current practically flows in alternate directions through 
the primary of the coil producing, it is claimed, an increase in the efficiency 
of the instrument. 

In all the instruments previously described, the diaphragm forms or 
is connected to one of the electrodes. A departure from this method is 
illustrated by the transmitter manufactured by The Sumter Telephone 
Manufacturing Company and shown in Fig. 89. 

The principal feature in this instrument consists of mounting 
the cell containing the granules and front electrode upon resilent springs, 
and, by means of two points or pins, transmitting the vibrations of the 
diaphragm to the cell. These pins are purposely located at points outside 
the centre of the diaphragm, preferably one third the distance between 
the centre and the edge thereof. 


COMMERCIAL TALKING EQUIPMENT 69 

Referring to the figure, A indicates the front plate or shell. Resting 
against this is the usual diaphragm D insulated therefrom by the oiled 
cloth ring E. 

Attached to the front plate A at four points, is the rear casing F, 
which is secured by screws G so that it can be readily removed. 



Secured to the rear casing F by two screws I are the springs H which 
extend towards the middle of the rear casing and are attached to the edge 
of a plate, shaped cell K, the inner side of which is platinum, and forms 
the front electrode. This cell contains the granular carbon. The cell is 
closed by means of a mica disc supporting the rear electrode. This disc 
is secured in place by the washer M; all of the parts including the springs 
H are secured together by the screw threaded ends of the two posts or 
pins J, which are secured by the nuts N. Two shorter screws and nuts are 
also used to securely close the cell. 

It will be noted that by adjusting the stationary electrode stem P in 
the support R, the tension or stress maintained on the resiliently supported 
cell K, and consequently the pressure of pins J on the diaphragm D may be 
varied to obtain the best results, and once this adjustment has been 
obtained, the instrument may be taken apart, the rear casing carrying the 
complete cell removed, and the diaphragm taken out and renewed, after 
which the instrument may be reassembled without adjustment. 

As all diaphragms are subject to corrosion, any means to enable their 
ready change constitutes quite an improvement in the instrument. 

By referring to the foregoing it will be observed that when sound 
waves strike the diaphragm, the latter is set in vibration, which is of 
greater force or amplitude at points beyond the centre. These amplified 
vibrations are transmitted to the pins J, J, so that the pins have an oscil¬ 
latory motion, which is conveyed to the cell K. 

The entire cell, together with its supporting springs being under 
strain, is peculiarly susceptible to the delicate vibrations of the pins, and 
the cell is caused to approach and recede from the rear or stationary elec¬ 
trode, which causes a variation of the current in the usual manner. 















70 


TELE PHONOLOGY 


It will be observed that the motion imparted to the cell is irregular in 
character owing to the pins being out of centre with respect to the cell, 
therefore the vibrations transmitted from the main diaphragm, instead of 
being uniform as is the case with transmitters connected to the cell at a 
single point, is irregular and uneven, and the consequent variation in the 
pressure on the granules considerably increased. 

In the majority of transmitters the tendency of the diaphragm is to 
vibrate inwardly when actuated, and to return to a neutral or central posi¬ 
tion after each impulse. 

In this transmitter, owing to the cell being held under tension, the 
tendency of the diaphragm is to vibrate in and out. Instead of tending to 
only increase the pressure from a normal point, the pressure is increased 
and diminished thereby causing a much greater current variation. 

The normal or “at rest” resistance is not as small as when the dia¬ 
phragm is actuated and moved inwardly, nor as great as when the dia¬ 
phragm springs outward, owing to the pressure of the cell supporting 
springs. 

The actual construction of the instrument embodies several features 
of merit. The necessity for dampening springs is avoided, the pressure 
on the diaphragm being applied through the two pins by the cell supporting 
springs. 

The rear casing encloses and protects the cell and supporting springs. 
The screws I, I are insulated from the rear case by rubber bushings, and 
one of these screws is arranged to serve as one terminal of the instrument 
and connects the circuit to the front electrode without the use of a fine 
wire, which is easily broken and hard to re fasten. 

The rear electrode is held by a support R, which is insulated from the 
rear casing and which also carries the other terminal. 

The pins J and J are provided with small hard rubber tips where they 
rest on the diaphragm, and consequently the diaphragm is not electrically 
connected. This is the first transmitter employing this form of construc¬ 
tion. 

From the above it will be seen that the frame or case, and diaphragm 
form no part of the circuit, which at all times is confined entirely to the 
cell and electrodes. 

As the cell is fastened with small nuts and screws, it is easy to disas¬ 
semble. This however is seldom if ever necessary. 

The usual form of back shell is used when the transmitter is 
mounted on standard wall or desk sets. When mounted on the small iron 
box residence type of phone, the ordinary back shell is omitted, the inner 
rear casing serving to perfectly protect the parts, as only the terminals are 
exposed. 

Owing to the increased action secured by this construction, the instru¬ 
ment can be given quite a high resistance without sacrificing the efficiency. 
This results in a saving in battery consumption. For long distance work 
three cells may be employed, and it is said that some remarkable results 
in long distance transmission have been secured with this instrument. 

By adjusting the position of the rear electrode stem, any degree of 
pressure on the diaphragm can be secured, thereby enabling “side tone” 
adjustments to be easily accomplished as the instrument can be made more 
or less sensitive as occasion demands. 

The various types of instruments so far described are typical of 
modern practice. To illustrate every type that has been invented would 




COMMERCIAL TALKING EQUIPMENT 71 

be a hopeless task as there are at present (1908) about two hundred and 
fifty patents granted on this piece of equipment, the majority of these 
being variations of the general types herein described. 

Current consumption is a vital point to be considered in local battery 
transmitters. A low resistance transmitter will necessitate renewing the 
batteries every few months; with a transmitter of moderate resistance, 
the batteries, will last twice as long. It is necessary to use an instrument 
of comparatively low resistance to secure the necessary efficiency, but in 
a great many instruments on the market owing to greed for volume this 
has been carried too far—the result is a quickly exhausted battery, and 
consequent expense. 

By using especially prepared carbon and electrodes, it is possible to 
produce an instrument possessing ample volume and yet use a minimum of 
current. With an induction coil primary of 1 ohm and two ordinary dry 
cells in good condition, the average local battery transmitter will pass 
from .250 to .320 ampere. This should not be taken as representing the 
amount of battery necessary for operation. Some transmitters will talk 
very well with only .050 or .075 ampere. They will however, unless a 
resistance is placed in circuit with them, pass .200 or .300 ampere, when in 
actual use. Therefore some of the claims for efficient operation, and 
battery consumption, made for the same instrument is somewhat amusing 
when it is not what will operate the transmitter that counts, but what act¬ 
ually passes through the instrument. 

The method of adjusting solid back transmitters varies but little 
among the different types, it being customary to loosen set screw holding 
the back electrode stem. The transmitter should then be talked into, and 
after the granules are shaken up by this, the set screw is tightened. This 
really means that the transmitter is self-adjusting. 

It will be found more practical to return defective transmitters to the 
factory for repair, except when the trouble is due to an accumulation of 
corrosive matter between the diaphragm and the front shell of the trans¬ 
mitter. This can easily be remedied by cleaning same and placing a new 
rubber band on the transmitter diaphragm, but if the trouble is in the 
adjustment of the transmitter such as the position of the buttons or elec¬ 
trodes, or the granular carbon, etc., or a fractured mica diaphragm, it is 
much better to return the transmitter to the factory. Several of the later 
types have eliminated the rubber band entirely and substitute a non-rot¬ 
ting oiled cloth, as previously described. 

Some manufacturers have made it a practice to cover the front of 
their transmitter with a sheet of thin celluloid to render same impervious 
to moisture. This is of course necessary whenever the construction of 
the transmitter is such that a crack or seam exists in the front of the 
instrument through which moisture could penetrate to the vital parts. 
One very satisfactory method of eliminating the trouble due to corrosion 
is to coat the entire front of the diaphragm with baking enamel, same as 
a bicycle frame, which is glass hard and waterproof. 

The means provided for attaching the wires to the transmitters is an 
important item. It is best to provide machine screw terminals under 
which the cords leading from the telephone can be attached. It is pre¬ 
sumed these cords are equipped with eyelets or clips, but the terminals 
should also be of such construction that wires can be easily attached. 

In conclusion it might be said that only an instrument which is finished 
in the best possible manner should be used. It is now customary to nickel- 


72 


TELEPHONOLOGY 


plate or black oxidize the parts such as the bridge, terminal screws, etc. 
in the better class of instruments. It might be said that a very good indi¬ 
cation of the quality of a telephone factory’s product may be arrived at by 
close scrutiny of their transmitters and receivers, and it will be found that 
the factory devoting the greatest care and attention to details in the 
manufacture of transmitters will prove reliable in many other respects. 

INDUCTION COILS.—The function of the induction coil as used in 
connection with the telephone was described in chapter one. A brief 
review of this will not be out of place, however. 

The simplest telephone line imaginable would consist of two receivers 
connected in series as shown at A, in Fig. 90, but such a circuit is only 
good for a short distance, as the currents generated are too feeble to 
transmit the speech intelligently for any distance. 

The invention of the transmitter, or electrical valve, rendered it 
possible to talk over a much longer distance. This, in addition to the trans¬ 
mitter and battery at each station resulted in the arrangement of the 
circuit as shown at B, Fig. 90. To obtain any results with this circuit it 
was necessary to connect the receivers so that the battery current flowed 
through them in such a manner as to strengthen the pull of the magnet 
on the diaphragm. 




Fig. 90. 

In this circuit, the effect of the current passing through the transmit¬ 
ters will be approximately proportional to the changes in the total current 
traversing the circuit. These changes are produced by the variations 
which the transmitters offer to the flow of electricity from the battery 
due to the increase and decrease of the resistance in the transmitters 
caused by the sound waves striking the diaphragms, thereby varying the 
distance between the electrodes. 

A circuit of this kind can be divided into several parts which prevent 
the flow of electricity. 

First: There is the resistance of the line wires, which vary according 
to their length, material and size. This is principally ohmic resistance. 
We will assume that this portion of the circuit does not exceed 50 ohms. 


























COMMERCIAL TALKING EQUIPMENT 


73 


Second: There is the resistance of the batteries. 

Third: There is the ohmic resistance of the receivers, which are 100 
ohms each. 

As the receiver coils are wound on iron cores, their inductance is 
high, and the actual resistance they offer to the high frequency voice 
currents is considerable. 

Fourth: There is the variable resistance of the transmitters which 
ranges from a fraction of an ohm to 50 or 60 ohms. 

From this it will be seen that a line, as previously described, may 
offer a resistance as high as 2000 ohms, owing to the impedance, while 
its ohmic resistance is not more than two or three hundred ohms. We 
will suppose the transmitter is capable of varying the resistance of the 
circuit 2 ohms. It will then be able to change the resistance of the circuit 
about one two thousandth of its value, which is all the power it possesses 
to change the total current flowing. Owing to this, and the low voltage 
of the current, the results are not satisfactory over lines ordinarily met 
with in exchange work. 

The induction coil was applied to the telephone by Thomas A. Edison 
in 1878 with a view to improving this condition. Fig. 90 at C shows a 
line with the coils in circuit with the transmitter and battery. The 
“primary” winding “P” (so termed because it is associated with the 
primary source of power, the battery) consist of a few turns of wire of 
low resistance, while the “secondary” coil, (so termed because secondary 
or induced currents flow through it) has a much higher resistance, and is 
wound with a great many turns of fine wire. This is connected to the 
receiver and line. 

The induction coil accomplishes the following: 

First: It provides a circuit for each transmitter that can be arranged 
to possess low impedance, thereby allowing the variation in the transmitter 
contacts to form a large percentage of the total current flowing. 

Second: It removes both transmitters from the line circuit, there¬ 
by decreasing the total resistance of same. 

Third: As the transmitter is of variable resistance, its presence 
directly in the line is objectional: the induction coil removes this 
objection. 



Fourth: It greatly increases the transmitting power of the telephone 
as a whole. This can be illustrated by reference to Fig. 90a, where “A” 
represents the variation of current produced in the circuit when the 
transmitters, receivers and batteries are in series, while “B” represents 
the same line, under the same conditions, when induction coils are used. It 
will be seen that the variations produced are much greater with the 
induction coil. This is due to the fact that when by the action of the 
coil, a variation of current is produced between the primary and secondary 




74 


TELEPHONOLOGY 


windings, the variation is in proportion as the number of turns in the 
primary is to the number of turns in the secondary. That is: if there are 
10 turns in the primary, and 100 turns in the secondary, the ratio is 100 
divided by 10, and the increase in voltage is 10. If two volts be applied 
to the primary and one ampere of current flows, the volts at the terminals 
of the secondary will be twice the secondary turns divided by the primary 
turns, and the current will be 1 multiplied by the primary turns, divided 
by the secondary turns. 

The loss due to the resistance of the line is proportional to the square 
of the current which is employed, while the current transmitted is pro¬ 
portional to the product of the volts times the amperes. Therefore by 
increasing the voltage, the same amount of energy may be transmitted at 
less loss. Owing to the fact that the transmitter will burn if the voltage 
is increased, it is impossible to operate it except with a low voltage cur¬ 
rent, but by using the induction coil, the low voltage large current of the 
primary or local circuit, is transformed into a small current at a high 
voltage in the secondary, which will overcome the line resistance and cause 
sufficient current to pass to operate a receiver over the longer lines. 

There are no satisfactory methods of mathematically determining 
the proper proportion for induction coils. Coils vary widely in their 
construction, a wide difference in size and number of turns often giving 
satisfactory results. In actual practice induction coils are manufactured 
for the particular instrument they are to be used with, and the usual 
method of determining the best induction coil for a given instrument 
is to test several different types and select the best. 

Induction coils are usually assembled by taking two fibre or wooden 
heads, and glueing or otherwise fastening a paper tube between them. 
The paper tube is then filled with as much fine iron wire cut the proper 
length, as it will hold, No. 24 being the usual size. This wire should be 
tightly packed in the tube, in which it is securely held in place by driving 
two or three small iron brads into the core wires, thus spreading them 
apart. Soft iron wire should be used for the core, avoiding the use of 
short lengths and bent pieces. 

While the heads can be made of wood or some other suitable material, 
fibre is preferable. The terminals should be of brass or German silver. 
Machine screws are sometimes provided for easily attaching the wires. 

The primary winding in the majority of coils consists of not more 
than three layers of wire ranging in size from No. 22 to No. 28, the 
resistance of the primary ranging from .39 to 1-1/2 ohms. The primary 
is covered with a layer of paper, and the secondary winding is begun. 
This consists of a wire ranging from No. 28 to No. 34 gauge, cotton or silk 
insulated, varying in resistance from 18 to 250 ohms. The outside of the 
coil is then covered with paper, the wires are soldered to their respective 
terminals, and the coil may be considered complete. 

One type of coil which is accepted as standard by some of the largest 
manufacturers, is of the dimensions shown in Fig. 91. Heads 1 inch or l 1 /# 
inch square. The primary consists of 240 turns of No. 26 B. & S. G. 
single cotton covered wire put on in 2 layers. The primary is covered 
with one layer of paper. The secondary consists of 2160 turns of No. 
28 B. & S. G. single silk covered wire. The primary has a resistance 
of .9 ohm, and the secondary 24 ohms. This coil is used for local battery 
or magneto work. 


t 


COMMERCIAL TALKING EQUIPMENT 75 

It is well to make the primary of as high resistance as possible with¬ 
out lessening the efficiency of the coil, as this decreases the drain on the 
battery. It is also well to keep the resistance of the secondary as low as 
possible when the coil is used in bridging telephones, as when a high 
wound coil is used, the voice currents are hindered from passing through 
the coil by the impedence of same, and are, therefore, forced through the 
ringers. 



Fig. 91. Fig. 92. 


A coil with a secondary resistance of 250 ohms wound on the same 
spool as shown in Fig. 91 has the same primary, and a secondary with 
12 layers of No. 36 B. & S. G. single silk covered wire. 

The generally accepted belief is that coils having small cores and 
small windings give better results than coils with large cores and high 
resistance windings. While the large cores give louder transmission, it 
is poorer in quality. In making experiments of this nature is should be 
remembered that in talking over a large coil at the transmitting station 
to the small coil at the receiving station, the small coil at the receiving 
end will always give better results than when two small coils are used 
together, while the small coil will generally show less efficiency when 
the positions are reversed, owing to the added impedance of the high 
winding of the large coil. 

Two small coils however, all things considered give better results 
than two large ones. It has been found by testing, that when the same 
kind of coils are used at each end of a line, the large coils give louder 
results, but the speech is not as distinct as when the small coils are used, 
as the transmission with the small coil is considerably clearer but some¬ 
what weaker. As it is clearness of speech that is desired, the small coils 
are therefore the best. 

Different chucks for holding induction coils while they are being 
wound are shown in Fig. 92. These chucks can be held in a hand drill 
clamped in a vise; or a regular winding machine or small lathe can be used. 

All makes of magneto coils are wound in the same direction, i. e., 
the primary and secondary are both wound without reversing the position 
of the coil. 

The arrangements of the terminals on various makes of induction 
coils is somewhat confusing, as it will be seen by reference to Fig. 93, 
which shows three coils, “A”, “B” and “C”. At “A” the primary winding 
is connected to terminals 1 and 2, and the secondary to terminals 3 and 4, 
each set of terminals being located on the respective heads. At “B”, one 
secondary terminal is located on one head of the coil, while the two pri¬ 
maries and other secondary are located on the other end of the coil. At 
“C” one secondary is on one end of the coil, while one primary and 
secondary are connected together and attached to one of the terminals on 


































76 TELEPHONOLOGY 

the other end of the coil, and the last primary is also connected to a ter¬ 
minal on the same end. 

Fig. 93a shows how the coils may be connected so as to accomplish 
the same purpose. The usual type of wiring is shown, and from this 
figure it will be noted that coils A, B, or C, are interchangeable although 
the terminals are different. 



The construction of a magneto coil is shown on the right, Fig. 93 
The primary wire is wound directly on the paper tube, or the core is 
covered with paper and the primary winding is begun. After the primary 
winding is finished several layers of paper are placed over it, and the 
secondary is then wound to the desired resistance. The complete coil 
is covered with paper or book-binder’s cloth, which should be shellacked to 
render it moisture proof 



Fig. 93a. 


One method of comparing induction coils is shown in Fig. 94. Here 
the switches, “A”, “B” and “C” are connected to various induction coils 
as shown. After the equipment is connected up, the listener at “R” hears 
a person, or the phonograph at “T” speak, and by increasing the resistance 
“X”, the comparative efficiency of the coils can be ascertained. 
































































































































COMMERCIAL TALKING EQUIPMENT 77 

The type of coil with two windings as just described, is the only one 
used in commercial telephone equipment. Various coils with three or 
more windings have been tried, but except for special purposes, have not 
come into general use. 

A coil with three windings is shown at A Fig. 95. Over the usual 
primary and secondary windings is placed a third winding consisting of 
the same (or more) turns as the secondary. This third winding is termed 
the “Tertiary”. 

For telephone instruments the coil is connected as shown at A. 
The line connecting to secondary, and receiver to tertiary. 

Sometimes an additional receiver is placed in circuit at X. The prac¬ 
tice of using two receivers is quite common in some European countries 
and this method of using an additional receiver without inserting same 
in the line current is sometimes used. It would seem that simply placing 
both receivers in series with an ordinary coil, would prove as satisfactory 
a method as any. 

When the circuit shown at A, Fig. 95 is used with noisy lines, owing 
to the receiver being removed from the direct line circuit, a slight gain 
in freedom from foreign noises is observed. This circuit however, is not 
quite as efficient for receiving as the ordinary two winding coil. 



Fig. 95. 


The arrangement shown at B, Fig. 95 is often used with switchboards 
and the three winding coil gives perfect results. The Teritary winding 
is connected to the Monitors or Managers desk and enables them to “listen 
in” without the knowledge of the operator, as closing the circuit of the 
Tertiary winding does not affect the side tone of the operator’s set to the 
same extent that closing the secondary circuit does. Operators are often 
enabled to tell when some one is observing their work, by listening for this 
“side tone” which the use of the three winding coil eliminates. 

The coil shown at C, Fig. 95 represents an attempt to arrange the 
telephone circuit so that leaving the receiver off the book would not affect 
ringing on the line. The secondary is wound in the usual manner and cut 
at the centre, or two wires are run on the coil side by side. The latter 
method is to be preferred. 

As the two parts of the secondary winding are in inductive relation 
to each other, in coming high frequency voice currents will be repeated 
from one to the other, thus establishing a circuit through the receiver in 
the usual manner. 

The ringing currents, owing to their low frequency, will not have 
sufficient effect on the coils to cause a flow of current, in fact the gap in 
the winding acts like an open circuit, to the generator currents, thereby 
enabling the phone to be rung even if the receiver is off the hook. 

As this arrangement accomplishes nothing more than a repeating coil 
or transformer effect, a loss is present both in transmitting and receiv¬ 
ing. Tms arrangement is now seldom used, condensers of 14 or Vi M. F. 





















78 


TELEPHONOLOGY 


capacity being inserted in the receiver circuit. These accomplish the 
same result with much less loss. 

Other arrangements of the windings have been tried, such as dividing 
the coil in the middle and winding the primary on one end, and secondary 
on the other; putting the primary on top of secondary; putting an addi¬ 
tional primary over the secondary, and connecting both primaries in 
multiple, etc.; but none of these methods have ever proven superior to the 
standard type for regular service. 

The coils used in magneto switch boards and common battery tele¬ 
phones will be described elsewhere in connection with the equipment they 
are used with. 

The tests for and location of trouble in induction coils is very simple. 
The usual fault is an open secondary winding, which can be easily ascer¬ 
tained by connecting the coil in series with a generator and bells. If it is 
impossible to ring through the coil, the secondary is open. An open pri¬ 
mary can be tested in the same manner. Aside from this fault in the pri¬ 
mary or secondary windings, trouble seldom if ever happens in properly 
constructed coils. 

It is always best if a coil is suspected of being in trouble, to simply 
change the coil for a new one, as sometimes it may have short-circuited 
layers which are not easy to locate, but cause a perceptible falling off in 
transmission. 

The Receiver, Transmitter, and Induction Coil are the parts of the 
complete telephone used in receiving and transmitting speech. The com¬ 
plete Telephone instrument consists of a combination of talking and ring¬ 
ing parts, and is described in the next chapter. 



Early type of Single Pole Receiver. 










CHAPTER IV. 


MAGNETO INSTRUMENTS AND CIRCUITS. 


The complete telephone instrument is a combination of the talking 
and ringing equipment, mounted in a suitable cabinet which is adapted 
(in magneto instruments) to accommodate the transmitter batteries. 

As the various parts have already been described, only their circuit 
connections and general assembly to form a complete instrument will be 
discussed. It should be remembered when a series or bridging instru¬ 
ment is described, that the generator, shunt, ringer coils, etc., are adapted 
for series or bridging work, as the case may be. 

Little need be said regarding the details of the complete instrument 
such as locks, hinges, cabinet work, etc. These parts have of late years 
been so perfected that little if any cause for trouble in them exists. The 
old style lock has given place to the more reliable screw fastening, thus 
enabling the door of the instrument to be opened readily. Any one 
could open the old style of lock formerly used, by removing the escutcheon 
plate with a screw driver, so the lock was really of no value. Should it 
be necessary to seal a modern instrument equipped with screw fastening, 
it is simply necessary to cover the head of the screw with sealing wax 
and stamp a monogram or other seal which cannot be easily imitated, 
therein. Usually two screw fasteners are provided, at the top and bot¬ 
tom of the door. 

The hinges in all modern instruments are provided with spring con¬ 
nections between the sides so that a metallic connection is formed which 
does not pass through the joint. This applies where the hinges are used 
as part of the circuit across the door to the ringer or other parts. The 
hinges are now seldom used in the talking circuit of the. instrument, a 
flexible cord being used instead, thus making an unbroken circuit directly 
from the transmitter to the other parts. 

The instrument is usually installed by fastening same to the wall, 
and the holes in the back board through which the screws pass should 
be protected by metal eyelets which prevent the back board splitting in 
case too large a screw is used. 

If there are wires in grooves in the back board, the grooves should 
filled with bees wax to nrevent trouble in case the instrument should 
be mounted on a damp wall, which might cause a ground if the wire was 
exposed. 

The finish of the cabinet has really nothing to do with the operation 
of the instrument, but the manner in which it is put together has. The 
wood should be well seasoned and so joined that there is no possibility 
of it ever coming apart. 


( 79 ) 




80 


TELEPHONOLOGY 


Quartered sawed oak is probably the most generally used wood. 
Walnut has been extensively used, but is rapidly going out of use owing 
to its scarcity. 

The use of metal cabinets is rapidly becoming general, especially in 
hospitals and other places where it is necessary to frequentlj 7 cleanse the 
instruments from disease germs. The metal cabinets can be washed 
with solutions which would prove fatal to polished wood work. 

Fig. 96 shows the compact type cabinet now in general use for 
magneto equipment. A 5 bar instrument is shown and the cabinet does 
not differ, except in width, when a 3 or 4 bar generator is used. The 
general arrangement of the parts is well shown in the illustration, and 
various makes differ but little from the one shown. In some makes the 
shelf supporting the generator is omitted, the generator being mounted 
on a bracket attached to the backboard. Sometimes the induction coil 
is mounted on the door instead of in the upper part of the cabinet. 



Fig. 96. 

Fig. 97 shows another type of cabinet which possesses some advan¬ 
tages. The arrangement of the various parts is as shown, the batteries 
being placed in a compartment at the bottom of the cabinet as shown in 
Fig. 98. This type has the advantage of a good writing desk, and also 
resembles modern common battery instruments, so that the set may be 
readily rewired in case the system is changed from Magneto to Common 
Battery, without the instrument looking out of place when compared 
with the regular Common Battery type. 

While the general arrangement of series and bridging circuits has 
been discussed, the usual types of wiring will be shown together with 
some special circuits, to show that by rearranging the various parts, 
nearly any desired result may be accomplished. 

Fig. 99 shows the old series circuit. When the receiver is off the 
hook, the generator and bells are completely cut out of circuit. Fig. 100 
shows a later type. When the receiver is on the hook, the receiver cir¬ 
cuit is short circuited and a clear circuit through the bells and generator 












MAGNETO INSTRUMENTS AND CIRCUITS 


81 


exists. When the receiver is off, the generator and bells are short cir¬ 
cuited. The advantages of this arrangement is that the bells are never 
completely cut off, for if the bottom hook contact fails, the incoming ring¬ 
ing current could find a path through the receiver, and the line would 
not be open which is the case with the first circuit, should the bottom hook 
contact fail. 



Fig. 97. Fig. 98. 


In both of these arrangements the generator winding is normally 
short circuited by the shunt springs. The ringers are from 80 to 250 
ohms resistance, the latter being more suitable for exchange work where 
there is only one instrument on a line. 


\l 




Bat. 




»P •< s 
-ft < E 
'i SC 


Hook 


hikioeh 


L -oo 





■ GEM. 




Z. //v-f; 



The usual bridging circuit is shown in Fig. 101. The talking cir¬ 
cuits are the same as in the series. The bells and generator are bridged 
across the line, the generator winding being normally open. 

6 . 


























































82 


TELEPHONOLOGY 


The circuit shown in Fig. 102 is often used. The generator is 
equipped with shunt springs so arranged that the ringer is short circuited 
when the generator crank is turned, which prevents vibrations from the 
gongs producing unpleasant ringing noises when the receiver is taken 
off. This also removes the ringer from the circuit, thereby lessening 
the load. 

In some makes of bridging instruments the generator shunt springs 
are so arranged that the armature winding is normally short circuited, 
which, it is claimed, prevents damage to the winding from lightning and 
other sources. 





%jr===x> 


F/G/OZ 



Generators in bridging instruments have from three to six bars or 
magnets, depending upon the class of service they are intended for. 

Line conditions such as length, size wire, etc., determine to a great 
extent the number of instruments that can be placed on one circuit. The 
fact should be always kept in mind that as all the bells ring at once, great 
confusion will result if more than a reasonable number of instruments 
are used. 

The actual number of instruments it is possible to operate on one 
line is only limited by the power of the generators and sensibility of the 
ringers. One manufacturer claims that 4 bar 1000 ohm ringer instru¬ 
ments will operate satisfactorily 12 per line, and if 1600 ohm ringers 
are used, 20 per line, and that 5 bar 1600 ohm instruments will operate 
25 per line, or more, depending upon line conditions. 

1600 ohms is becoming a standard resistance for bridging ringer 
movements. The 1000 ohm ringers ring strongly but only a few can be 
put on one line without using very powerful generators. 2000 and 2500 
ohm ringers do not give a very loud ring, the stroke being rather weak 
owing to the small amount of current that can force its way through the 
high resistance coils. The 1600 ohm ringer gives a sufficiently powerful 
ring to insure satisfaction, and permits the maximum number of instru¬ 
ments to be placed on one line. 

For short lines with only five or six instruments, 3 bar generators 
can be used with success. A three bar bridging generator has a lower 
resistance winding of larger size wire, and greater output than a series 
generator. 

Four bar generators are the standard r or bridging service, and the 
greatest number of instruments it is practicable to operate on one line 

may be successfully rung with them. Where line conditions are very 

« 













































MAGNETO INSTRUMENTS AND CIRCUITS 


83 


severe, or where a large number of instruments are used, 5 bar genera¬ 
tors are desirable. 

All instruments on the same line must have ringers of the same 
resistance. The generators may have 3, 4 or 5 bars as this will not have 
a general effect on the line, the generators only being in circuit when 
the crank is turned. 

It is perhaps needless to state that series and bridging instruments 
cannot be used on the same line. While the talking equipment of the 
instruments is the same, the series ringer is of such low resistance that 
it practically short circuits the entire line for ringing if bridged on, 
while if put in series it will probably not get sufficient current for its 
operation. 

Of course instruments of different makes can be used on the same 
line if of the same resistance. It should be remembered that one ineffi¬ 
cient instrument will affect all the others to some extent, and it is there¬ 
fore better to have all the instruments on the same line of the same 
make, selecting equipment of known quality. 

On bridging lines when a receiver is accidentally left off the hook, 
or when a person wilfully listens in, it is impossible to ring over the line 
to other instruments, as the entire line is disabled owing to the low resist¬ 
ance path formed from one side of the circuit to the other, through the 
secondary and receiver of the telephone where the receiver is off. 

To remedy this evil a small condenser is inserted in the receiver cir¬ 
cuit, as shown in Fig. 103. The condenser offers high resistance to ring¬ 
ing currents and low resistance to talking currents, which makes it pos¬ 
sible to ring any telephone on the line regardless of the number of receiv¬ 
ers left off the hook. This attachment in no way affects the talking quali¬ 
ties of the instrument. Sometimes the condenser is mounted in a small 
box and connected to the telephone as shown in Fig. 104. This enables 
the condenser to be attached to the telephone without changing the inter¬ 
nal connections of the instrument in any manner, as the condenser is 
put in series with the receiver by means of the extra cord, as shown. 



Several manufacturers of this device claim that on a line of twenty 
instruments eighteen of them may have the receivers off the hook, while 
the two remaining instruments can ring each other without trouble. 

Condensers for this purpose are usually small in size and of *4 or 1/2 
M. F. capacity. Nearly all standard makes of bridging telephones are 
furnished wired for condensers, which can be easily put in lator if 

















































84 


TELEPHONOLOGY 


required. Condensers can be used in the secondary circuit of nearly all 
bridged talking circuit instruments. 

It is often desirable to have bridging telephones so wired that a sub¬ 
scriber can call the central office for all connections or for other parties 
on the same line, thereby giving the operator a chance to keep a record 
of all calls made. Such service is very advantageous. The subscribers 
are not required to give their own signals, which is a difficult feat for 
some to perform, and the calling of the exchange does not ring the other 
bells on the line which in a great measure prevents the curious from lis¬ 
tening in. 

To accomplish this a so-called “direct current” generator is wired 
in the circuit as shown in Fig. 105. The current delivered from this gen¬ 
erator is of such a nature that it does not affect the ringers bridged across 
the line. The generator is of the regular type with the addition of a 
small commutator on the end of the armature shaft which is so placed 
that only one pulsation or alternation is given for each revolution of the 
armature. This current being always in one direction will not ring 
the bells bridged on the line but will throw the drop signal in the Central 
Office. The drop should not be of more than 100 ohms resistance. A 
condenser can be placed in the receiver circuit of this instrument, same 
as shown in Figs. 103 and 104. 



It is sometimes desirable to arrange this circuit so that the phones 
can call each other or central, separately. When this is done a genera¬ 
tor is used designed to give both pulsating and alternating current. An 
ordinary bridging drop is used at central, and an extension bell is also 
bridged on the line. By simply turning the crank on the phone, alternat¬ 
ing current is generated which rings the bells on the line, the bell at cen¬ 
tral, and throws the drop. As both bell and drop at central are operated, 
the operator need not answer, as it is apparent that some one on the line 
is wanted. 

Each phone is equipped with a push button which when pushed, 
connects pulsating current to the line instead of alternating. This pul¬ 
sating current will not ring any of the bells, but will throw the drop, 
and the operator, seeing the drop fall without the bell ringing, will know 
the call is intended for the central office, and can answer. The cir¬ 
cuit of the instrument using both alternating and pulsating current is 
shown in Fig. 106. 

Pulsating or so called direct current generators are further described 
on page 178. Both the above methods can be used with either grounded 
or metallic lines. 

















































MAGNETO INSTRUMENTS AND CIRCUITS 


85 


A peculiar method of calling central without ringing the phones on 
the line, for use with grounded systems, is shown in Fig. 107. An ordi¬ 
nary ringer is taken and the clapper ball is removed. To the striker 
rod is soldered a piece of tin about 11/2 inches square. The ringer is 
mounted on a suitable piece of board, and the square piece of tin is 
allowed to project into a glass of ordinary kerosene oil. A contact is 
arranged to make connection with the'striker rod when same is moved 
all the way to one side and a counterbalance weight is put on top of the 
striker, all as shown in Fig. 107. 





This arrangement is bridged on the line at Central. The drop is 
connected as shown. The generators in the telephones on the line are 
equipped as shown in Fig. 106. The telephones call each other with 
alternating current by turning the crank without pushing the button, and 
alternating current traverses the line in the usual manner and rings the 
bells bridged thereon. At the same time the ringer at Central is operated, 
but owing to the immersion of the square piece of tin in the oil, the 
clapper will not move sufficiently in one direction to close the contact X. 

When it is desired to call Central from one of the phones, the button 
is pushed and the crank turned, this delivers pulsating current to the line, 
which will not affect the ringers bridged thereon, but as it is a current 
operating in one direction, the ringer at Central if connected in the proper 
manner, will draw its armature to one side thereby closing the contact 
X; as soon as this is closed, the drop is bridged across the line and is 
immediately thrown. It will be observed that it is necessary to so con¬ 
nect the special ringer at Central that the pulsating current will flow 
through same in the proper direction to pull the armature to the proper 
side and close the contact X. This arrangement is easily made, and 
when properly constructed gives satisfaction. 

Figs. 105 and 106 are particularly adapted 'or calling Central sepa¬ 
rately from the telephones over grounded lines. When metallic lines are 
available, a circuit using the regular alternating current generator and a 
push button may be used. This is shown in Fig. 108. 

When the button is pushed current traverses one line only and the 
ground, passing through the drop at Central and operating same, as 
shown in Fig. 109. It will be noted that there is no circuit from one line 
to the other, and consequently the bells in the other telephones on the line 
do not ring. 

When the crank on any ’phone is turned without pushing the button, 
the current traverses both of the line wires as shown in Fig. 110, and 








































































86 


TELEPHONOLOGY 


rings the bells bridged thereon, but the drop at Central does not fall as 
there is no circuit to the ground. 

It is sometimes desired to use ordinary Bridging telephones not 
equipped with the buttons, for this system. These can be easily arranged 
to work in connection with a single pole double throw knife switch, 
arranged to connect one side of telephone to ground or to line, as desired. 
This arrangement is shown in Fig. 108a. 




Fl<r.|08*. 


Care must be taken to connect these instruments in such a manner 
that when the button is pushed the generator current is connected directly 
to that side of the line to which the drop is connected at the Central Office. 
If this is not done, the current will pass through all the bells bridged on 
the line to get to the proper side of the line to find a circuit through the 
drop. It is simply necessary when connecting the ’phones to try them 
with the lines in one position, and if they are not properly connected, 
reverse the lines. 

While the system described above is perfectly satisfactory for use in 
most localities, still where there are high tension power circuits in prox¬ 
imity to the telephone line, some noise will be caused by the line being 
unbalanced by reason of one side being connected to ground through the 
drop. When it is desired to eliminate this trouble, it is customary to 
equip the ’phones with a 5-spring push button arranged to short circuit 




both the lines, connect one side of the generator thereto and connect the 
other side of the generator to ground. The lines are brought into an 
impedance coil at the Central Office; to the center of which is connected 
the line drop as shown in Fig. 111. This impedance coil may consist of 
an ordinary ringer with the armature screwed down against the pole 


OH 

LINE 


















































































MAGNETO INSTRUMENTS AND CIRCUITS 


37 


pieces. From the center point, where the two coils are joined together, 
run a tap to one side of the drop which should be about i00 ohms resist¬ 
ance. When a button is pushed, current flows over both sides of the line 
and the ground, and throws the drop. As the drop is connected to the 
center or neutral point between both the lines, the amount of ground on 
each side of the line is equal and a balance is thereby preserved. 

Another method is to make the drop winding in two parts, as shown 
at A, Fig. 111. The centre point is connected to ground. Care must be 
taken to secure an equal number of turns of the same resistance for each 
winding. The windings must also be placed on the core in opposite 
directions so that when a current is traversing the line wires (as when 
the ’phones on the line call each other) it will not throw the drop owing 
to one winding opposing the other. 


/// - 



When putting up the ’phones equipped with the five spring buttons, 
it is not necessary to do any testing out to locate each side of the line. 
Connect ’phones same as an ordinary Bridging line. 

It will be observed when using either of the above arrangements 
for calling Central by means of push buttons, that there is no ground on 
the line when a plug is in the jack at the Central Office, and that talking 
is at all times metallic, thus enabling the highest class long distance service 
to be given with ’phones equipped in this manner. 

When the arrangement shown in Fig. 109 and 110 is used the clear 
out drop may be bridged across the cord circuit and the middle point 
of the winding grounded. The drop will then respond when a button is 
pushed. 

The two parts of the winding need not be in opposition to each other, 
simply ground the centre point of a winding all in one direction. 

This arrangement of the clear out drop cannot be used when the 5 
spring buttons are used, in which case the clear out drop is operated by 
giving one short turn of the generator crank without pushing the button. 
This will cause all the bells to ring, but this is not a great disadvantage, 
as the conversation would be completed and listeners would only be 
notified of the termination of a conversation and not its beginning. 

The common method of wiring wall sets is to use bare tinned copper 
wire of from 19 to 22 gauge, run in grooves in the back board and brought 
through holes at the proper points for connection to the various parts. 
The grooves are filled with beeswax and this protects the wires from 
moisture and holds them in place. The use of staples to hold the wire in 





















































88 


TELEPHONOLOGY 


position should be avoided and all splices should be made inside the cabinet 
where they can be seen. The use of bare tinned wire is preferable to the 
use of cotton-covered or “Annunciator” wire, as with the latter, if the 
wire is broken inside the insulation, the break is very hard to locate. 
With this method of wiring in grooves, a wire is rather hard to trace and 
inspect, it being necessary to remove the telephone from the wall. 

Lately the “Cable wiring” method has come into extensive use. 
Double silk and cotton insulated wire is used, of the same high grade as 
used for switchboard key cables. Each wire has a different colored insula¬ 
tion and the wires are formed into a cable and placed in the cabinet. The 
connections to the various parts serve to hold the cable in place, and the 
ends of the wires connecting to generator, coil, etc., are equipped with clip 
terminals. As each wire is a different color and in plain sight, testing is 
facilitated. The circuit arrangement of the instrument can also be chang¬ 
ed very easily as the cable is usually only soldered to the hook springs ana 
hinges. By this means the grooves and holes in the back board are 
eliminated and the wiring is more compact and neatly arranged. 

One company which has furnished several thousand instruments 
wired in this manner, report that less trouble results from lightning than 
when bare wire is used. The possibility of short circuits is also lessened, 
as the cables are boiled in beeswax and shellacked. 



Fig. 112. 



Figs. 112 and 113 show the series and bridging circuits of cable wired 

sets. 


The portable Desk Telephone or Stand, has always been a very 
popular type, but its high cost of maintainance has prevented it from 
coming into comparatively extensive use. 

As a Desk Stand is portable, it naturally receives more handling and 
rough treatment than a wall instrument. The cords being necessarily 
flexible are also subject to wear. As the parts must be more compact than 
in the wall type, stability and strength is o r 'ten sacrificed to weight and 
neatness of appearance, thus rendering the instrument weak mechanically, 
short lived, and hard to maintain. 

Recently great improvements in the mechanical construction of Desk 
Stands has taken place, so that many of the instruments now offered are 
not only graceful in design, but also rigidly constructed and assembled 























































MAGNETO INSTRUMENTS AND CIRCUITS 89 

i 

in such a manner as to be free from complication and as easy to maintain 
as the average wall set. 

Typical of modern practice is the Desk Stand furnished by The 
Sumter Telephone Mfg. Co., and shown in Fig. 114. 

The base is formed from stamped steel and is enameled or nickle 
plated. A heavy stamping is mounted vertically in the centre of the base 
and supports the transmitter and hook mechanism. A split stem encloses 
the hook contacts, this casing and in fact all parts of the instrument 
being insulated from the circuit. 



Fig. 114. 


To inspect the hook contacts, the knurled nut at the top of the casing 
is loosened, as shown in Fig. 115, this permits the removal of the stem 
casing, which exposes to view the entire hook mechanism, as shown in 
Fig. 116. 



Fig. 115. Fig. 116. 








90 


TELEPHONOLOGY 


The hook contact springs are arranged to play between stops of hard 
rubber, which keep them in permanent adjustment. A separate spring 
is used to raise the hook lever, which is not dependent upon the tension of 
the contact springs for its operation. This raising spring is of round 
steel, enameled, and can be adjusted to properly operate the hook with 
any weight of receiver. 

The Hook lever is made removable for ease in shipment or in case of 
breakage, by attaching same to the hook mechanism with a screw as shown 
in Fig. 117, which clearly shows how the lever may be removed or a new 
one inserted without readjusting any of the other parts. 

In this type of stand, only the cord terminals are located in the base, 
the induction coil and other parts being mounted in the Magneto Box. 



Fig. 117. Fig. 118. 


Access is obtained to'the base of the Stand by taking one screw out of the 
center of the enameled steel felt covered bottom, which when removed 
exposes to view the cord terminals and connections to hook springs and 
other parts. 

From Fig. 118 it will be seen that standard tips are used on both ends 
of the cord. 

Wires are soldered to the cord terminals and connect to the hook 
springs, receiver cord terminals and transmitter. There are no sliding or 
contact connections used in this stand which is entirely operative with all 
wiring and every part in view, when the casing and bottom are removed. 

The bells, generator and induction coil for use with the stand are 
assembled in a small box, the complete outfit being shown in Fig. 119. 
The line, battery, and cord terminals are located upon a strip located 
upon the left side of the box and holes are provided for the entrance of 
the cord and wires, by this means all terminals and connections are 
enclosed. 

The Dean Elect. Co. use a different method of assembling the various 
parts, and combine them so that they are readily removable from each 
other. Fig. 120 shows a Dean stand disassembled. The vertical upright 
carrying the transmitter and hook lever, is provided at the bottom with 
a catch which holds it in place. When in place the notched lever connected 
to the receiver hook engages the hook contact springs which are placed in 
the bottom of the stand, moving them sideways. 










MAGNETO INSTRUMENTS AND CIRCUITS 91 

The flexible wires from the transmitter terminate in two contact pins 
which engage springs in the base of the stand, when the stem is placed 
in position. From this it will be seen that the stem carrying the hook 


Fig. 119. 

lever and transmitter can be unlatched and removed entire from the stand 
without unfastening any wires. 


Fig. 120. 


The bottom of this stand is removed by inserting a screw driver blade 
in a slot and turning to the left, this exposes all the parts except the hook 
lever, which is removed from the upright tube by pressing a release spring 
as previously described. 







92 


TELEPHONOLOGY 


A very original feature of this stand is the interchangeable circuit 
plate shown in Fig. 121. This carries all the wiring of the stand except 
the two cords to the transmitter. The induction coil, hook springs 
and cord terminals are mounted on this, so that each stand is complete so 
far as the talking parts are concerned. This circuit plate may be removed 
and another substituted, arranged for Common Battery, should a-change 
from one system to the other ever be made, this change accomplishing a 
complete rearrangement of the circuits. 

In this stand the base is provided with a leather ring to prevent mar¬ 
ring furniture. This takes the place of the felt often used in other makes, 
and is very durable. The stem of the stand is covered with a hard rubber 
sleeve, and the base is either nickled or black enameled. 

The magneto box used with this stand is similar to the one shown in 
Fig. 119 except that it only contains the generator and ringer. A cord 
rack or small terminal block is provided to which the line, battery, and 
magneto box connections are brought and connected to the cords. A 4 
conductor cord is standard with this company for series and bridging 
work, the series circuit arrangement being shown in Fig. 122 and the 
Bridging in 123. In the latter circuit the ringer is short circuited when 
turning the crank. 



Fig. 121. 


The two instruments just described will serve to show that the Desk 
Stand has reached a high state of development, and will compare favorably 
with wall sets as to cost of maintainance. The two types shown illustrate 
the two prevailing methods of assembling the parts. In one type the Desk 
Stand carries the hook switch, transmitter, and receiver only, while in the 
other type all of the talking equipment is carried in the stand. 

The circuit combinations possible with Desk Stands are as numerous 
and varied as with the wall type. The following will serve to illustrate 
some in common use, in addition to the series and bridging circuits of the 
Dean set, shown in Figs. 122 and 123. 

Fig. 124 shows the circuits of the Stand when the coil is mounted in 
the magneto box. A 5 conductor cord is used to permit using the stand 
for either series or bridging work. The magneto box wiring is quite 
unique and is shown in Fig. 125. Four wires are brought to the generator 
terminals, upon the connection of these depends whether the set is series 
or bridging. 






MAGNETO INSTRUMENTS AND CIRCUITS 


93 


For Series, the slate and green-white wires are connected to genera¬ 
tor. For Bridging the red and and slate wires connect together and to 



Fig. 122. 

one generator terminal, and the brown wire to the other. The marking 
of the terminals and colors of the wires enables the circuits to be readily 
traced. 












































































































































94 


TELEPHONOLOGY 


Sometimes it is desired to use a Desk Stand as an extension instru¬ 
ment, without bells or generator. With stands of the type carrying the 
coil in the base this is accomplished by simply omitting the magneto box. 
With the type of stands not carrying the coil it is necessary to provide one 
mounted on a block as shown in Fig. 126 which shows the line and battery 
connections. 

Should it ever be necessary to add a magneto, this can be done by 
attaching same to the two posts provided, otherwise nothing is connected 
to these posts. 

Condensers can be used in the receiver circuits of desk stands by put¬ 
ting them in series with the receiver. Any of the special circuits described 
in connection with wall sets can be used by simply rearranging the desk 
set circuit connections, for this reason they will not be described here. 



The location of troubles in the complete telephone instrument are com¬ 
paratively simple if sound judgment is used as to their proper location. If 
the instrument will not talk, it is folly to examine the generator and ringer, 
and if there is ringing trouble it certainly will not be found in the transmit¬ 
ter, induction coil, or receiver. 

In locating trouble in Desk sets, the cords are the first part that 
should be thoroughly examined. If a scraping noise is the trouble, 
examine each cord tip where it is joined to the conductor, as often this 
joint is imperfect or a loose connection formed. 

If a break is suspected in the conductor, the cord should be discon¬ 
nected from the stand, and each conductor tested by placing same in series 
with a receiver and battery. Shake the cord, and if the conductor is par¬ 
tially open, a scraping noise will be heard. 

The use of a receiver for making general tests should appeal to every 
trouble man on account of the simplicity of the operation. It is only neces¬ 
sary to place a cell of battery in series with the receiver to locate breaks 
or opens, by placing the suspected wire in series with the receiver and bat¬ 
tery. 

Hook contacts that are suspected of not closing properly, generator 
shunts, push button contacts—in fact any wire or contact can be easily 
tested in this manner. 

Coils and windings of all descriptions may be tested by this method 
but some practice is necessary to secure accurate results, as a coil can be 













































































MAGNETO INSTRUMENTS AND CIRCUITS 


95 


completely open and yet a click will be heard in the receiver owing to the 
inductive relation between the two parts of the broken winding. 

The majority of desk stands are now equipped with transmitters in 
which the working parts are insulated from the shell. When this is the 
case, sometimes through the failure of the rubber band on the diaphragm, 
or failure in the insulation of the other parts, the transmitter will “go 
short” on the metal frame of the stand, and cause trouble. This is easily 
located by testing the transmitter or changing same. 

This trouble also occurs at the hook switch, the insulation between 
the circuit springs and the hook lever mechanism becoming defective. 
This is located by testing with a magneto bell. 

The best practice would seem to be that of completely insulating every 
current carrying part from the frame of the stand, as this will prevent the 
user from receiving a very unpleasant shock, which can and does happen 
should the user be standing on a damp floor and pick up the stand before 
the operator had ceased ringing on the line, especially if a power genera¬ 
tor is used and one side of same is grounded. 

Often desk stands are placed on the top of steam radiators or other 
metallic bodies connected to the earth. This often happens in offices 
where the radiator is near a window and forms a convenient place to keep 
the stand. If the stand is not insulated, as soon as the protecting felt on 
the bottom becomes worn, the line becomes grounded as soon as the stand 
, is placed on the radiator. In magneto work this does not matter so much 
but in Common Battery exchanges it is a source of great annoyance and is 
hard to locate and still more difficult to prevent, unless the instrument 
is insulated. 

Tests for the location of troubles in the various parts have been 
described, but a few general tests will be given. When testing an instru¬ 
ment, first disconnect the line wires, otherwise the trouble may be in the 
line or house wiring and not in the instrument. Modern instruments 
have reached such a state of perfection that nine out of ten troubles 
reported will be found in the line and not in the instrument. In the fol¬ 
lowing tests the line wires are supposed to be disconnected from the in¬ 
strument. 


BELLS DO NOT RING WHEN OTHERS CALL. 

With receiver on the hook, turn crank; if the bell rings, bell is O. K.; 
if not, bell needs adjustment or is burnt out by lightning, or small wire 
leading into bell coils is broken. If series, connect line posts together 
before testing. Examine hook contact. 

Place fingers across line posts and turn crank; a smart shock should be 
felt which indicates that ’phone wiring to line posts is 0. K. If series, 
short circuit Ringer before testing with fingers for generator current. 

YOU CANNOT RING ANYBODY. 

Test with the fingers as explained above. If you do not feel any cur¬ 
rent, and if you can’t ring your own bell, the generator is out of order. 
See that spring on left-hand end of generator makes good contact with 
axle of wheel when crank is turned, or generator may be burnt out by 
lightning. If generator turns hard, winding may be short circuited or 
insulation between shunt springs is bad. 


96 TELEPHONOLOGY 

YOU CAN HEAR OTHERS, BUT THEY DO NOT HEAR YOU. 


Examine the batteries. Left-hand wire in ’phone should go to zinc 
post or can of battery; then carbon post or post on rod in center of can 
should go to zinc post of next battery; the last carbon post should go to 
clip on cord which goes to transmitter. All connections must be tight. 
Batteries don’t last forever. When you use the 'phone, the batteries are 
being used up, and where use is frequent, batteries only last six or seven 
months. 

Connect line posts together with wire, lift off receiver and speak into 
transmitter. You should hear yourself talk perfectly and loud. If talk 
is weak, the batteries are probably exhausted. Examine hook contacts; 
hook springs should come together firmly when hook goes up. Examine 
connections on induction coil, see that all connections are tight. 

YOU CAN TALK TO OTHERS BUT CANNOT HEAR. 

Connect line posts together and proceed as above. If you can hear 
yourself talk, ’phone is O. K. and trouble is in line. If you cannot hear, 
examine receiver cord, which is probably broken. Unscrew ear piece of 
receiver and note if diaphragm is bent or dented; if so, get a new one, as 
you can’t straighten it. Dust out receiver and screw cap firmly in place. 
Be sure and replace diaphragm right side up. Examine hook contacts. 

If a new receiver cord does not help, try a new receiver; if this does 
not cure the trouble, the induction coil is probably burnt out by lightning, 
or there is a broken wire in telephone. 

SPUTTERING NOISES WHILE YOU TALK. 

Connect line posts with piece of wire. Talk into transmitter and shake 
receiver cord; also test transmitter cord and all connections, some¬ 
times too much battery (never use more than 3 cells) will cause a frying 
noise. If ’phone talks clear without noise, look for trouble in loose joint 
in line. 

Always clean Lightning Arrester, removing carbon dust (if any) 
from between line and ground plates. This dust often causes trouble 
and this should be the first part to be examined. 

One important part of the complete instrument which has not been 
previously referred to, is the Lightning Arrester. This is usually located 
upon the top of the cabinet in Wall sets. Desk sets are not equipped with 
arresters as a rule, because the magneto box, upon which the arrester 
would be placd, is often mounted underneath desks and in other locations 
near inflammable materials liable to become ignited if the arrester should 
spark heavily, which often occurs. 

Early types of Arresters consisted of two metal plates with saw tooth 
edges, connected to each line binding post. The saw teeth were placed 
close to another plate having similar teeth, this plate being connected 
to the ground. A hole was provided for inserting a metal plug, so that all 
three plates could be connected together, thereby grounding the line. The 
plug was often placed in the arrester and forgotten, thereby putting the 
instrument out of business and, on bridging lines, disabling the entire 
line. 


MAGNETO INSTRUMENTS AND CIRCUITS 


97 


The saw tooth arrester is shown in Fig. 127. Owing to the teeth being 
of metal, serious arcs and flashes took place if the arrester was subjected 
to a heavy discharge, and sometimes the teeth would melt together, per¬ 
manently disabling the instrument. An improvement in this device 
consisted of making the ground plate of carbon, which is a non fusible 
substance capable of withstanding severe currents without melting. This 
resulted in the arrangement shown in Fig. 128 which is typical of the 
form of Arrester with which all modern wall sets are equipped. 

The Carbon disc is kept from coming in contact with the line plates by 
the mica disc. This disc has a number of holes punched in it to provide 
a ready path for the lightning discharges, which are supposed to jump 
from the metal line plates to the carbon ground plate and flow to ground, 
without passing through the instrument. 




Sometimes fuses are combined with the arrester. The fuses consist 
oP short pieces of easily fusible wire, and are placed in series with the 
incoming line, usually before it reaches the Arrester. As a protection 
against lightning, fuses are practically worthless, the lightning often 
burning out the instrument without disturbing the fuse. 

When the telephone line is exposed to crosses with wires carrying 
heavy currents, fuses are necessary as they protect the instrument against 
such currents, and a combined carbon and fuse arrester is advisable, but 
where lightning protection only is necessary, fuses will be found worse 
than useless, as they are often blown by slight discharges without serving 
any purpose except to put the telephone out of service until they are 
replaced. 

The Lightning Arrester usually forms part of the line terminals 
on the telephone and the ground terminal, or one connected to the carbon 
plate is usually the middle one. 

On Metallic lines, the lines connect to the outside terminals and a 
ground wire to the centre, this wire serving only to act as a passageway 
for the escape of the lightning current from the Arrester. 

On grounded lines, one of the line terminals is connected to the 
ground terminal, and in this case the ground wire forms part of the ring¬ 
ing and talking circuit. The incoming line wire is connected to the other 
line terminal. 

As the wooden cabinet is not a good place on which to mount a piece 
of equipment which is liable to spark, and as the insurance regulations 
require these devices to be mounted on bases of non-combustible material 































98 


TELEPHONOLOGY 


and placed where the lines enter the building so as to protect the inside 
wiring as well as the instrument, some other device was necessary. 

This led to the development of the type shown in Fig. 129, which 
consists of three carbon plates separated from each other by perforated 
mica, the parts being mounted on a porcelain base. The outside plates 
connect to the line wires, and the centre plate to the ground. 

All of these arresters depend upon providing a path to ground for 
the lightning, which is supposed to jump across the space between the 
line and ground plates, instead of passing through the instrument. 

This, it will be observed is only a side path to ground, and sometimes 
the Arrester failed to work, owing to the current rushing by the Arrester, 



Fig. 129. 


a poor ground connection, or too great a space separating the ground 
and line plates. The space between the line and ground plates should not 
exceed .005 in. and less than this is better. 

When the mica is very thin, the carbon dust caused by the current 
passing between the plates, often causes a ground on the line. The 
blocks should therefore be frequently removed from the Arrester and 
cleaned. 

It will be seen that all types of Arresters arranged with plates adja¬ 
cent to a grounding medium, do not offer any opposition to the lightning 
entering the telephone, but only offer a path to ground, so placed that 
under favorable conditions the lightning would take this path, instead of 
continuing on into the instrument. 



Fig. 130. 


An Arrester offering direct opposition to the passage of lightning 
currents through it, is shown in Fig. 130. Two coils, each convolution of 




























MAGNETO INSTRUMENTS AND CIRCUITS 


99 


which forms a rectangle, are inserted directly in the circuit between the 
line and the telephone. The core around which the coils are formed, is 
of carbon, and the coils are prevented from direct contact with same by 
strips of mica which only leave the edges of the square blocks exposed. 
These cores are connected to the ground. The operation of this device 
is as follows. 

When the incoming lightning reaches the Arrester it encounters the 
coils, which are in the circuit between the line and the instrument. 
Lightning currents are alternating in character and possess enormous 
frequency, therefore when they encounter the coils which have many 
abrupt turns and convolutions, their progress is greatly impeded. 

At each bend in the coil, the tendency of the lightning is to follow a 
strait line, it therefore flies off, which action is helped by the presence 
of the grounded carbon blocks which attract and take the charge, carry¬ 
ing it safely to ground. 

A lightning discharge abhors a conductor having kinks or abrupt 
turns, therefore the coils act to choke back the current and prevent its 
entrance to the telephone. In addition, the coils are in close proximity 
to a grounding medium which deflects and safely carries the current to 
ground. 

The coils have a resistance of only a fraction of an ohm, and do not 
offer any appreciable resistance to talking and ringing currents. 

The principle used in this Arrester, that lightning will not pass 
through a coil having abrupt turns or angles, readily explains why ringer 
and other coils are sometime destroyed by comparatively slight lightning 



Fig. 131. 


discharges, as the wire is very fine and cannot stand the strain of the tre¬ 
mendously high frequency current which is always seeking to travel in 
a straight line, consequently the wire is disrupted. This o'ten occurs 
without the coil being actually burnt, the wire having the appearance of 
being broken. 

The arrester shown in Fig. 130 is known as the “Multi Discharge” 
owing to the numerous discharge points offered for the escape of the 



100 


TELEPHONOLOGY 


lightning. There are several types, the one shown in Fig. 130 being a 
lightning arrester only, for use on lines not exposed to crosses with wires 
carrying heavy currents. Other types of this device are equipped with 
fuses of the open or enclosed types. A fused type is shown in Fig. 131, 
the lines are connected to the fuse end. 

Figs. 132 and 133 show the Multi Discharge arrester connected on 
grounded and metallic lines. Many of these arresters are extensively 
used in rural line work, as they are free from troubles due to the collec¬ 
tion of carbon dust between the line coils and ground blocks. While the 
space between the coils and blocks is only .003 or .005 in. this space is 
open, and the dust is free to fall out, in fact it is blown out by action of 
the slight flash which accompanies the operation of the device. 

Later models of the Multi Discharge arrester are provided with 
covers which completely enclose the working parts. 

The Multi Discharge Arrester was the pioneer choke coil device 
especially designed for telephone use. Several other Coil Arresters are 
now offered, but these use a circular coil, and usually place the grounding 
medium on the outside of the coil in the shape of a shell, usually of metal. 
None of these devices are especially efficient nor approach the original 




model in this respect, owing to the absence of the square coil having abi'upt 
turns or angles in every convolution. Upon this depends the efficiency of 
the device, and to ignore this is to ignore the principle upon which the 
device depends for its success ful operation. 

Careful attention should be paid to securing a good ground connec¬ 
tion for any type of arrester, otherwise the device will not operate per¬ 
fectly and the instrument will be damaged. 

The ground wire should not be of less size than No. 14 B. & S. guage 
copper wire, and should be free from short bends , curls or kinks; it should 
be as short and straight as possible. 

When it is necessary to make a turn, the bend should never have less 
than one foot radius. 

Support the ground wire on knobs from the arrester to ground con- 


































MAGNETO INSTRUMENTS AND CIRCUITS 


101 


nections. In towns where water or gas pipes are laid, connection can 
be made to them, and a good ground is assured. 

A soldered connection can be made, but for the water pipes, a clamp 
shown in Fig. 132a should be used. On gas pipes the wire can be wrapped 
as shown in Fig. 132b first filing the pipe bright, then solder the wire coils 
together and if possible solder to the pipe. 

In locations where no water or gas pipe is available, a ground rod is 
used. One satisfactory method is to take a piece of iron pipe, preferably 
galvanized, flatten one end and drive into the earth to the required depth, 
leaving about 6 in. above the ground, to this solder or clamp the ground 
wire. A ground connection must reach permanent moisture to be satis¬ 
factory. 

This is assured when connection is made to a gas or water pipe, but 
is not when a rod is used, unless the rod is driven deep enough to reach 
the damp strata under the surface soil. Usually six or eight feet is suffi¬ 
cient but in stony, clay, or sandy soils, especially in mountainous coun¬ 
tries, fifteen or twenty feet may be necessary. 


Fig. 132a. 

When connecting to gas or water pipes, never connect to a lead pipe, 
and always connect as near the street, or where the pipe enters the build¬ 
ing, as possible. 

If a gas meter is used, the ground wire must connect to the main pipe 
before it reaches the meter. Never connect to the house side of the meter. 

In some cases a connection can be made on the house side of the meter, 
provided a piece of wire is connected from the house to the street side of 
the meter thereby bridging or connecting across same so that a path is 
provided for the lightning and so that in case the meter is ever removed, 
no interference with the telephone ground will result. 

The location of troubles in lightning arresters are so apparent that 
they will not be described here. A ground caused by dust collecting 
between the line and ground plates is easily tested for by ringing across 
from one block to the other, and is remedied by removing the dust. 

An open fuse is easily located by bridging the terminals with a piece 
of wire and testing to see if the circuit is closed. 

All telephones connected to Aerial lines or cables, should be provided 
with arresters. Where the lines are entirely underground, as in some of 
the large cities, the usual practie is to omit the Arrester, as the lines are 
not exposed to lightning, and arresters are unnecessary. 

There is another device termed a “sneak circuit” arrester, used to 
prevent small continuous currents caused by the telephone line becoming 
crossed with other wires, from entering the instrument. These are 
described elsewhere. 






















CHAPTER V. 


MAGNETO SWITCHBOARDS. 


It soon becomes evident there is a limit to the number of telephones 
that can be satisfactorily operated on one line, therefore some means must 
be provided for connecting two or more lines together. A device of this 
nature is called a “Switchboard.” 

A simple arrangement of this nature for connecting two lines, is 
shown in Fig. 134. Ordinary switches are used. The lines are connected 
as shown, and an extension bell is bridged across each line to act as a 
signal. 

A telephone instrument is connected to the blades of the switches, and 
by throwing switch A or B the phone may be connected to line A or B. 
By throwing both A and B the two lines are connected together. 

One of the extension bells may be dispensed with by keeping the 
phone switch always on A or B and receiving the calls over that line on 
the bell in the phone. 

A better arrangement is shown in Fig. 136. A double throw key is 
used, and one bell only. When the key is thrown to the right, the phone 
is connected to the line coming in on that side, and when thrown to the 
left phone is connected to left hand line. When key is in the central 
position, the two lines are connected together. 



The bell on the switch box is always connected to the line which is 
not connected to the phone, so at no time is either line “cut out” but both 
lines can always signal the central phone regardless of the position of 
the switch. 

Another arrangement is shown in Fig. 135. Here a plug and jacks are 
used. The plug is a connecting pin having an insulated brass tip portion 
to which is attached one of the circuit wires, the sleeve part of the plug 
forming a terminal for the other circuit wire. The jack consists of two 
springs arranged to make contact with the two portions of the plue when 
it is pushed between them. The jack is arranged with two additional 

( 102 ) 




























MAGNETO SWITCHBOARDS 103 

spiings which break contact when the plug is inserted, and to which the 
extension bell is connected. 

inserting the plug in one or the other of the jacks, the telephone 
. connected to the respective lines, and the extension bell is left connected 
to the line not m use. By plugging into the centre jack C, the phone is 
connected to both lines at once. 

This arrangement can be used with as many lines as there are jacks 

F.Tfn ’ ai A lc , °f a Pair of plugs any two lines can be connected 

together A bell bridged across the cords will ring, thereby notifying the 
attendant when a disconnection is desired. 

The circuit arrangements shown in Figs. 134, 135, and 136 are for 
metallic lines, if used with grounded lines, a ground wire would be con¬ 
nected to the terminals marked g. This equipment is also supposed 
to be used with bridging lines. 




Fig. 137. 


Many uses for the three arrangements just described will occur to 
those operating two or more lines. Often a iong line may be cut in two, 
thus facilitating the use of same as both ends may be used at the same 
time. The ringing is also simplified as only one half the phones need be 
rung at once, thereby lessening the number of signals and load on the 
line. 

It will be seen that where a number of lines are brought together at 
one point, some compact arrangement is required to handle the connec¬ 
tions, as a number of the switches just described would prove too cum¬ 
bersome. A complete switch of the key variety, the circuit of which is 
shown in Fig. 136, is about 8 in. square and is illustrated in Fig. 137. Ten 
of these would occupy several square feet of space and are not as easy 
to operate as if the equipment was all in one cabinet. This led to the de¬ 
velopment of a more compact signal, which is commonly known as a 
“drop.” 

The earliest type of Switchboard signal or drop consisted of a coil of 
wire at the rear end of which was suspended an armature or piece of 
iron provided with a latch which projected forward and engaged a shut¬ 
ter, so placed that when the latch was raised by reason of the armature 
being drawn towards the coil, the shutter was released and fell down 
exposing a number in view of the operator, who thereupon plugged into 
the jack which was mounted separate from the drop in the lower portion 
of the board. An early form of drop is shown in Fig. 138. This is of 
the double coil type, the coil not being armored. When a number of un¬ 
armored drops are placed side by side cross talk may result caused by 
inductive leakage between the coils. To prevent this the coils are encased 
in armor, as shown in Fig. 139, the iron tube completely enclosing 
the coil and preventing any leakage of the magnetic lines. 












104 


TELEPHONOLGY 


With the unarmored type, the attractive power of only one pole 
of the coil is available and two coils are used, whereas, when the armor 
is placed on the coil, the pull of the coil on the armature is greatly increased 
as the armor forms one pole, and the end of the core the other, conse¬ 
quently only one coil need be used 




Fig. 138. Fig. 139. 

No doubt this drop is familiar to every telephone man, and that it 
is a very efficient arrangement, is proven by the fact that thousands are 
in use, especially by the Bell Companies, who developed this type to its 
highest degree o p perfection, both mechanically and electrically. 

The fact that the drop had to be restored after each call necessitated 
a great deal of work on the part of the operator, and therefore one of the 
first improvements was to combine the drop and jack so that the drop shut¬ 
ter was automatically restored by the insertion of the plug in the jack. 
This type of equipment has been on the market for a number of years, and 
exists in a great many forms which differ from each other only in mechani¬ 
cal construction, arrangments of the various parts, etc. The usual form 
of construction is such that the jack throat or opening is located immedi¬ 
ately below the drop shutter, and one of the jack springs is so arranged 
that it protrudes from the jack sufficiently to engage the shutter when in 
a fallen position, and the act of inserting the plug in the jack causes this 
spring to throw the shutter upwards, and thereby restores same. Some¬ 
times the plug restores the shutter by direct contact therewith, the spring 
being eliminated. 

The highest development o f this type of combined drop and jack may 
be illustrated by the Dean Elect. Cos. drop shown in Fig. 140. The drops 



Fig. 140. Fig. 141. 

are mounted on metal strips about 6*4 in* long X 1% in. wide each strip 
carrying five drops. The drop and jack are insulated from this mounting 
plate so that same is never any part of the talking or ringing circuits. 



MAGNETO SWITCHBOARDS 


105 


The drop winding which is really the only part requiring removal, 
is on a removable spool having a hollow core, and is designed to slip over 
a permanent core riveted into the drop shell and made a part of it, as 
shown in Fig. 141. This permits of a very efficient magnetic circuit being 
secured as the tube and core are practically one piece. 



Fig. 142. Fig. 143. 


The drop winding is provided with terminals as shown in Fig. 142, 
and the coil is simply slipped into the shell as shown in the figure, and is 
securely locked into position by a steel catch. The connection between 
the winding and the jack spring’s is accomplished by the connecting links 
or short punchings shown in Fig. 142, screws being provided for holding 
these as shown. 

Instead of removing the armature which would be necessary if same 
was held in place by pivot screws, it is hinged as shown in the figures, 
so that it can be swung up out of the way. A spring action similar to 
that used in a pocket knife blade is employed to hold the armature in the 
normal position in front of the drop core. This arrangement obviates 
the necessity of any adjustments being made when a coil is removed or 
replaced. 

Fig. 143 shows a drop with the coil in place. The wires are soldered 
to the small lugs provided with eyelets, shown connected to the jack 
springs. The wires can be removed from the jack by loosening the screws 
holding- these lugs and the necessity for unsoldering the wires is thereby 
obviated. 

The operation and details of the drop are evident from the illustra¬ 
tions. Fig. 143a shows the arrangement of the night alarm contacts, 
which are very positive in action. 



This drop well illustrates the present development of the self restor¬ 
ing combined drop and jack type o construction, when the armature is 



















106 


TELEPHONOLOGY 


located at the rear of the drop coil, and the shutter is released by a hook 
moving upward when the drop armature is actuated. 

Another type of combined drop and jack is illustrated by the drop 
made by the Monarch Tel. Mfg. Co., and shown in Fig. 144. 

The armature is mounted in front of the drop coil. When armature 
is actuated the shutter is released by the hook moving downwards. 

The action of the night bell springs is apparent from the figure, also 
the method of restoring the drop shutter. 



Fig. 144. 


Means for adjusting the armature is provided in this drop. The 
core of the coil is drilled to admit a long spring, the tension of which is 
regulated by the screw at the back of the drop, by turning this screw the 
tension on the drop armature may be regulated thereby making the drop 
more or less sensitive. 

The necessity for this adjustment is that sometimes it is desirable 
to have the drop buzz in unison with the number of rings given on the 
line, and by adjusting the spring, each drop can be adjusted to the varying 
conditions of each line. This makes this drop a signal ringing drop. 
Other types use a different arrangement, as will be described later. 



Fig. 145. 


Fig. 145 shows how the coil is removed. A pin in the coil head en¬ 
gages a slot in the armor and the coil is locked in place by giving same a 
slight turn to the right. The connection between the drop and the jack 
is made in a similar manner to that in the Dean drop. 

The combined drop and jack furnished by the Western Elect. Co. 
is shown in Figs. 146, 147, and 148. 






































MAGNETO SWITCHBOARDS 


107 


In place of the shutter employed in other drops, this type is equipped 
with a sphere revolving on a horizontal axis and so arranged that a por¬ 
tion of its surface projects through a round opening in the mounting 
plate; that part of its surface normally exposed is black, corresponding 
with the surface of the mounting plate. When the signal is operated, the 
sphere revolves on its axle, and the black portion moves up and disappears 
behind the mounting plate, leaving exposed a polished aluminum surface. 
The sphere projects from the face of the board a sufficient distance to be 
visible from either side. Fig. 147 shows the drop in a normal condition, 
and Fig. 148, when exposed. The sphere is filled with lead and always 
has a tendency to revolve until the white side is exposed. 

When a plug is inserted in the jack its tip raises the tip line spring. 
This acts on the restoring lever which turns the sphere to its normal posi¬ 
tion. 

These drops are wound to 500 ohms and the coil is armored. From 
Fig. 146 it will be evident that the coil is provided with soldered connec- 



Fig. 146. 


tions to the jack, and is removed by taking the pivot screws out of the 
armature, removing the same and withdrawing the coil from the armor 
casing. The arrangement of the other parts is evident from the illustra¬ 
tions. 

A type of drop of the “plug ringing” variety so called because ring¬ 
ing was accomplished by pushing the plug into the jack instead of using 
a key, is represented by the Sumter Type F drop shown in Fig. 149. This 
was a very satisfactory drop but is no longer manufactured, this Com¬ 
pany having replaced it with the more modern Unitype equipment. 


HOLDING PIN. 


i >ace pla tc 


UNOER CONTACT SPRING 


Fig. 147. 


/RE STORINGS 


NIGHT 8ELL CONTACT ATM 
ARMATURE 


target 



PLUG 














NlCHT BELL 
CONTACT SPRING 


LINE SPRING 


PLATINUM CONTACT 
^LINE SPRING 


Fig. 148. 


Re ferring to the fisrures, the construction and assembly of the various 
parts will be readily understood. The shutter is supported in its normal 






























108 


TELE PHONOLOGY 


position from the back by the rod attached to the armature. When this 
rod is raised by the armature being attracted by the drop coil, the shutter 
is released and falls inwardly thus causing the number to disappear from 
view as shown in Fig. 150. When the shutter falls inwardly it closes the 
night bell contacts N. N. ringing the night bell in the usual manner. 

The shutter is restored by the insertion of the plug in the jack, by 
the tip of the plug coming in contact with a small projection on the bottom 
of the shutter. 



Fig. 149. 


To ring on a line when using this drop, it was only necessary to put 
the plug in the jack and push same in as far as it would go. From Fig. 
151 it will be observed that the plug handle does not touch the front 
plate of the jack but is some distance from it, although the tip and sleeve 
portions of the plug engage the tip and sleeve springs of the jack so that 



Fig. 150. Fig. 151. 


a connection is formed in the usual manner. Now when the plug is 
pushed all the way in, or until the handle strikes the face plate, the rub¬ 
ber plunger P Fig. 150 (which is connected to a projecting piece T 
normally held in position by spring S) is pushed back and forces springs 
e, e, (which connect to the jack or line springs) upwards, where they 
contact on ringing strips F F, as shown in Fig. 149 and 150. 

The drop coil is removed from this drop by taking off the armature 
and loosening the screw connections from the jack springs to armature 
coil. The drops are secured in the board and the wires attached to them 
by means of the two projecting arms L. L which are equipped with nuts 
under which the line wires can be placed. 

On grounded lines the sleeve side of the jacks must be grounded. 

The chief objection to this type of equipment was the breakage of 
the plug cords, caused by the operator striking the butt of the cord with 





















MAGNETO SWITCHBOARDS 


109 


the palm of the hand when ringing. This was a very rapid board to 
operate, and this type of drop was very popular just before the Multiple 
Switchboard came into general use, as rapid service could be given. The 
wear and tear on the cords, plugs and jacks was such, however, that the 
type of equipment using ringing keys has entirely supplanted the plug 
ringing type. 

Of course when pressure is removed from the plug, it is returned 
to the normal position by the action of the spring S. When the plug 
is forced into the ringing position, the tip jack spring rides on the rubber 
insulation between the tip and sleeve of the plug, this opens the cord cir¬ 
cuit so that the generator circuit does not flow over same. 



Fig. 152. 


Fig. 150 shows that the generator is wired in multiple with the two 
metal strips F, and F. Under these strips is located springs e, e, which 
are normally out of circuit with strips F, F, but which are brought into 
contact with them by the act of pushing the plug into the jack as far as 
it will go. The current from the generator is then projected directly to 
the subscriber’s line without passing over the cord and plug, thus prevent¬ 
ing current “ringing back” through the waiting subscriber’s instrument. 
When through ringing and the plug is released, it automatically returns to 
the normal position in the jack, establishing the talking circuit. 

Fig. 152 shows the complete circuits of a board equipped with these 
drops. With the exception of the generator circuit, the wiring is the 



same as ordinarily used. The night bell circuit is carried into each drop 
by the springs N 2 and N 3 which connect to two vertical bars running 
between each vertical row of drops. These springs connect with springs 
N and N. 

Another modification of the idea of automatically restoring the drop 
by the insertion of the plug into the jack was to equip the drop coils with a 
































































no 


TELEPHONOLOGY 


double winding. One winding was connected to the line in the usual 
manner. The other winding was connected in series with a pair 
of contacts so arranged that when the first winding was energized and the 
armature drawn towards the core of the drop that this pair of contacts 
would be closed, and battery would be applied to the second winding which 
would hold the drop signal displayed until the call was answered, the sig¬ 
nal being de-energized by the separation of two contact springs located 
in the jack. This form of construction, while used to some little extent, 
is open to the objection of having two windings on the drop core, and 
necessitating the use of an extra pair of contacts in the jack, and this 
method also necessitates the maintainance of a battery at the Central 
Office, the function of which is to hold the signals displayed until the oper¬ 
ator answers same. The circuit arrangement is shown in Fig. 153. The 
shutter is arranged back of a mounting plate and is not displayed until 
lifted up by the armature. When this occurs contact C is closed and bat¬ 
tery is applied to the locking coil, which holds the armature until contact 
J is broken by the insertion of the plug in the jack. 



In this type of drop, the jack need not be mounted in close proximity 
to the drop, as it is evident that the act of plugging into the jack will 
restore the drop shutter without the plug having any mechanical connec¬ 
tion therewith. 

From the foregoing it will be seen that drop equipment may be divid¬ 
ed into two classes, that where the drop is separate from the jack, the jack 
being located in another part of the cabinet, usually some inches below 
the drop; and where the drop and jack are combined in one structure 
and permanently associated with each other. 

Another type of equipment is that where the jacks are assembled in 
strips, usually of ten jacks each, and the drops are unitary structures 
adapted to be placed in close proximity to the jacks without being perma¬ 
nently combined therewith. 

The Unitype drop, manufactured by The Sumter Tel. Mfg. Co. illus¬ 
trates this type, which is a very successful method of construction, one 
noticeable feature being the ease with which any drop can be removed 
from or inserted in the board without the use of tools or unfastening any 
wires. 

Fig. 154 shows a cross section of the drop, which is inserted between 




































MAGNETO SWITCHBOARDS 


111 


two strips of jacks. It will be seen that the usual coil “h” is connected 
to the inside contacts “k” of the jack immediately below the drop, by 
means of the two flexible springs “j” projecting from the back of the drop 
coil. When the armature moves inwardly by reason of the coil “h” 
being energized, the shutter “e” is released and drops through the slot 
in the front of the drop. When the plug enters the jack, the latch “g” is 
pushed inwardly and restores the shutter “e”. 

The dotted lines show shutter in the operated position. 



Fig. 155. Fig. 156. 


Fig. 155 shows a rear view of the drops and jacks and clearly shows 
the contact springs in the drop making contact with those in the jack, 
Fig. 156 shows a front view, drop No. 3 being in a normal condition, drop 
No. 4 shows the shutter exposed, and drop No. 5 shows the plug in the 
jack, the call answered, and the shutter restored. The small shutter 
which falls through the slot is white enameled, and makes a very striking 
signal against the dull black finish of the switchboard front. 

It will be seen that the operation of this drop depends upon the law 
of gravity, there being no springs or double windings and that the drop 
only has two moving parts, viz., the armature and the shutter. The 
armature is made with a knife edge, which engages a small wing or pro¬ 
jection on the foot of the shutter. This point of contact being very min¬ 
ute, the friction is reduced to a minimum. 

The use of pivot screws to support the armature, which are 
sometimes a source of trouble, is obviated in this drop by using rods upon 
which the armature and shutter are hung. These rods are simply slipped 
in and out of the shell, and are held in place by the end of the drop struc¬ 
ture which forms the front, and also laps about an inch on each side. By 
taking two screws out of the sides o ' the drop this end may be removed, 
the different parts are then entirely loose and may be taken apart and put 
together by hand. 

By reference to Fig. 154, it will be seen that the drop is equipped with 
two springs upon the top, these carrying the night bell contacts which 
are closed when the armature “f” is drawn towards the coil “h”, the arma¬ 
ture “f” being located in this position after having once been energized, 
by the small wing or foot on the shutter “e”. 

In Fig. 157 is shown a strip of jacks. The jack springs are punched 
from German silver, and should be long and flexible enough to ensure 
their making a secure contact without danger of bending. The inside, 
or cut-off springs of the jack are formed from solid brass. The contact 
edges are formed with an upturned knife edge which firmly presses 





112 


TELEPHONOLOGY 


against the jack springs with a tension of several pounds. This action is 
non-grinding, and yet a rubbing contact is secured. The jack springs 
are forced into the solid rubber mounting strip, and as no holes are 
punched in the springs, their elasticity is unimpaired. 

The form of construction in which the springs are mounted edge up, 
would seem to be superior to that in which the springs are mounted 
side up, as it is impossible for dirt to find lodgment in the jack, and as 
each jack strip is open at the top and bottom, the dirt can sift through 
the board and be blown out with a bellows. 

Nothing but the best hard rubber insulation should be used through¬ 
out a jack strip, and the metal parts of the jack strip should be heavily 
nickled, or polished and lacquered, so that corrosion is prevented. The 
numbers are usually formed by stamping same into rubber mounting face, 
and then filling them with white lead. 

The method of combining the Unitype drop and jack is as folllows: 
A metal mounting frame is provided in which all the jack strips are 
placed, this eliminates mounting anything on the woodwork which is 
liable to warp. One end of this frame is shown at “m” Fig. 158. 

The jack strips slide in the grooves cut in this frame, and a slotted 
punching n slips freely over the screw “o”. To remove a jack strip 
from the board, simply loosen “o”, move piece “w” anu pull the jack 
strip out. About 3 ft. of cable is allowed to each jack strip, this slack 
being formed up so that it does not occupy much space. This being the 



Fig. 157. 



Fig. 158. 


case, each strip can be removed about three feet from the board without 
unsoldering any of the wires attached thereto. The drops are placed 
upon the mounting plate, “c” and are locked in place by the two project¬ 
ing contact springs on each drop which connect with the inside contacts 
of the jacks. From the above, it will be seen that a drop can be instantly 
inserted or withdrawn from the front of the board by simply pulling it. 
out, as there are no wires to disconnect or screws to remove, this feature 
being shown in Fig. 159. 

The drop coil may be removed by loosening one screw and pulling the 
coil out of the case, as shown in Fig. 159a. Removing and replacing the 
coil does not change the adjustment of the drop mechanism in any man¬ 
ner nor is it necessary to unsolder any wires. 

The improvements in drop construction have greatly reduced the 
cost of maintainance on Central Office equipment, not only this, but the 
lines do not have to remain out of service any length of time, as the oper- 



















MAGNETO SWITCHBOARDS 


113 


ator or other inexperienced person can remove a bad drop from a work¬ 
ing line, and substitute therefor a good drop from a line which is not 
working. 

With the Unitype model, it is often possible to substitute for one of 
the line drops which may be injured, one of the clear-out drops, which 
can be withdrawn and used temporarily as a line drop. This will in no 
way affect the cord circuit from which the clear-out drop is removed, 
except that no ring-off signal will be secured. As no numbers appear on 
the drops, a drop is readily interchangeable to any part of the board, the 
numbers being placed adjacent to the jacks. 



Fig. 159. Fig. 159-a 


The majority of modern Switchboards are numbered from 0 to 99 
for each operator’s position, beginning at the lower left hand corner of 
the Switchboard. This makes the numbering uniform throughout a large 
board, and as 0, 10, 20 30, etc., are always the left hand end numbers on 
each position, the location of the number is made very easy for the opera¬ 
tor. 

While the drops and jacks are a vital part of the Switchboard, the 
operator’s equipment is also of the utmost importance. A detail to be 
care ully considered when purchasing equipment, is the construction of 
the cords and plugs. 

Fig. 160 shows the construction of a standard plug. The tip “r” is 
riveted to a steel stem which is thoroughly insulated from the sleeve or 
body of the plug, by means of a hard rubber bushing running it’s entire 
length. To prevent the tip which is riveted to the stem from turning, a 
pin is driven across the entire plug and is insulated therefrom by hard 
rubber. 



One trouble sometimes met with in plugs is that as the plug enters 
the jack the sleeve spring will wear the rubber insulation between the 
tip and sleeve. To prevent this in the type of plug shown in the illustra¬ 
tion, a brass ring “n” is placed on the rubber bushing in such a manner 

8 











114 TELEPHONOLOGY 

that at no time can the jack springs cut into the rubber and cause trouble. 
The different positions the jack springs assume as the plug enters the 
jack is shown by the dotted lines. 

The plug cord is connected to the plug by screwing same into the 
threads provided in the brass shank of the plug. The tip conductor of 
the cord is provided with an eyelet so arranged that it fits easily under 
the screw placed in the lug going to the tip. The fiber sleeve “x” slips 
over the plug and forms a handle, being held in place by a small screw. 
The ends of the cords attached to the Switchboard are equipped with ter¬ 
minals as shown in Fig. 161 which renders their connection very easy. 
The insulation of the sleeve conductor is usually marked with a colored 
trace thread which enables the cords to be attached to the Switchboard 
in a uniform manner. 



The ringing and listening keys associated with the cord circuits are 
described elsewhere, but in selecting these it is well to pay the greatest 
attention to securing a type of key in which the springs are long and 
flexible, and good contact is assured. There are several types of equip¬ 
ment on the market in which the keys can be readily removed from the 
board as shown in Fig. 162, as each key has an individual set of wires 
about 6" long, which allows the key to be removed from the Switchboard 
without unsoldering any connections. 

A standard operator’s head receiver is shown in Fig. 163. It is the 
usual double pole variety with the various parts made as small and com¬ 
pact as is consistent with securing the best results. 

The usual method of mounting the operator’s transmitter is to fasten 
same to adjustable cords which are equipped with weights which balance 
the transmitter, and cause it to stay in any position it may be placed. 
This arrangement will be noticed on the various cuts of Switchboards 
herein shown, but the more modern and efficient breast operator’s set as 








































MAGNETO SWITCHBOARDS 


115 


shown in Fig. 164, is to be recommended where the operator is constantly 
at the board, for several reasons, the principal one being that the trans¬ 
mitter always remains the same distance from the operator’s lips irre¬ 
spective of what position she may be in. Also there is nothing between 
the operator and the face of the board, and her vision is therefore unob¬ 
structed. 



Fig. 162. 

When the breast type transmitter is used, a plug with 4 contacts and 
a jack with a corresponding number of springs is used, two of these con¬ 
tacts carrying the circuit to the transmitter and two to the receiver. 

When the suspended type transmitter is used, the operator’s receiver 
jack usually has 4 springs, two of which engage the tip and sleeve of the 
operator’s receiver cord plug, see Fig. 165. The other two or inside 
springs, connect in series with the operator’s transmitter in such a man¬ 
ner that when the plug is inserted in the jack, they close together and 
thereby allow the battery to flow through the transmitter. When the plug 


Fig. 163. 




is withdrawn the springs open. This type of plug is adapted for use 
with cords having standard tips, thus obviating the use of special cords. 
Operator’s cords are usually 6 ft. long. 





116 


TELEPHONOLOGY 


The line circuit in magneto boards varies but little among different 
manufacturers. The drop may be wound to a resistance varying from 
80 to 1600 Ohms. The prevailing practice is to wind Series drops to 
100 Ohms, while Bridging drops are usually wound to 500 Ohms. It has 
been found with modern methods of completely enclosing the drop wind¬ 
ing in a shell, that 500 ohm drops possess sufficient impedance, and it is 



Fig. 164. 


Fig. 165. 


seldom that a higher winding is either necessary or desirable. As a rule, 
the larger the wire used, provided the proper number of turns and re¬ 
sistance is secured, the better, as the finer the wire, the more liable it is 
to damage from lightning and other causes. 



The usual line circuit is shown in Fig. 166. Here it will be seen that 
the drop winding is cut off from the line circuit when the plug is inserted 
in the jack. This is also accomplished as shown at Fig. 167, where one 
side of the winding is cut off, which accomplishes the same result. 



| 


,DttOP ACANATOtte. 



cot of*- r'P^.k.Nsb- 


DROP COR-C- 

DROP 3rtOTTeR HOOK.. 
DROP injTTtfa,. 
v.-^noTTec aesroarNO 

oPRino 

X»ACr; TIP 6PRI.N6. 


3K LOCAL tVVT T 6 BY T fc L* PHON *r 
A.T £*T 


Fig. 167. 








































MAGNETO SWITCHBOARDS 


117 


It should be remembered that although a Switchboard may have a 
capacity of 100 or more lines, each line circuit with its drop and jack is 
exactly the same, the only difference between a 100 and 500 line board be¬ 
ing the number of circuits. 

All modern Switchboards are wired for full metallic circuits, and, of 
course, may be used on either common return or grounded system. In 
case the board wired for full metallic service is to be used on grounded 
systems it is simply necessary to connect one side, preferably the sleeve 
side, of the line jacks to the ground or common return. 

A common trouble with drops is their failure to fall when a subscri¬ 
ber calls. This can be the result of a short circuited drop, a bad con¬ 
tact between the springs of the jack, an open wire in the cable leading 
into the Switchboard, or an open drop winding. It is, of course, pre¬ 
sumed that the line leading into the exchange is O. K. up to the point 
where it joins the switchboard cable. 

In testing for trouble in the switchboard it is best to connect an ordi¬ 
nary telephone directly to the pair in the cable leading to the switchboard. 
If upon ringing, the drop does not fall, one of the plugs on the switchboard 
should be inserted in the jack. Then ring again. If the clear-out drop 
connected to the cord in use, falls, it is an indication that the pair in the 
switchboard cable is O. K. up to the jack. The jack should then be exam¬ 
ined to see if the inside springs or ones which connect with the drop, 
make contact with the long springs when the plug is withdrawn. If this 
seems to be O. K., a receiver should be connected directly to the terminals 
of the drop coil winding. If upon turning the crank of the telephone, the 
sound o e the generator can be heard in the receiver, the circuit is O. K. 
to the drop terminals and it is likely the drop coil is open, and same should 
be taken out and repaired. 

Most of the trouble in line circuits is caused by open drop windings, 
lightning generally being the cause of this. Every switchboard should 
be equipped with some form of lightning arrester, which will pay for 
itself in the saving of drop coils inside of a few months, especially in 
localities where electrical storms prevail. 

It will be apparent that the falling of a drop is hardly sufficient noise 
to attract the operator’s attention, and some additional means must there¬ 
fore be provided. This is accomplished by equipping each drop with a 
pair of contacts so arranged that when the drop shutter falls, the con¬ 
tact will remain closed, thereby ringing a bell, which continues ringing 
until the operator restores the drop. This bell is termed the “Night 
Bell”, on account of its usually being used at night when no regular opera¬ 
tor is in attendance. 

The usual form of night bell circuit is shown in Fig. 168. When prop¬ 
erly constructed, very little trouble occurs, but drops in which the circuit is 
closed through a hinge should be avoided, as a great deal of trouble has 
been experienced with drops so constructed. By referring to Fig. 168, 
it will be seen that when the shutter is down, the contact spring closes 
the circuit through the bell and battery. One objection to this circuit 
is that the drop contacts become dirty, the current flow is thereby hin¬ 
dered and the bell fails to ring. This necessitates either increasing the 
battery or constant cleaning of the drop contacts. To increase the bat¬ 
tery means more sparking, and this causes corrosion and more trouble. 
Usually no more than two cells of battery should be used for the night 


118 


TELEPHONOLOGY 


bell circuit. It may be said, however, that the majority of the drops 
now on the market are provided with contacts so constructed that very 
little, if any, trouble from this cause occurs. 

To guard against the occurrence of this trouble, it is customary to 
insert a relay wound to about 500 Ohms in series with a 12 volt battery, 
as shown in Fig. 169. It will now be seen that when the drop falls, the 
current flows through the relay and drop contacts back to the battery. 
This closes the relay, and the bell which is in circuit with the relay con¬ 
tacts will ring. It will be observed when this device is used, that the 
action of the night bell is entirely dependent upon one set of contacts 
in the relay which can be pointed with platinum and which are easy to 
adjust, so that instead of having to adjust each individual drop contact 
it is only necessary to adjust a single contact in the relay. The great 
advantage of this arrangement however, lies in the fact that relay is 
exceedingly sensitive to minute currents, and will therefore close, even 



Fig. 168. 



/*/lot Las** • sM Vd.rs 



Fig. 169. 


if the contacts in the drops are very dirty. A relay of this description 
wound to 500 ohms, with a 12 volt battery or 8 ordinary dry cells, will 
close through a resistance of 2000 Ohms, which is more than the night 
bell would ring through even if 8 or 10 cells of battery were used, con* 
nected in the usual manner. Owing to the high resistance of the relay 
very little current flows, consequently there is no sparking at the drop 
contacts, which remain bright and clean. 

Another desirable feature can be obtained when the relay is used. 
This is the use of pilot lamps. The night bell, of course, is very desirable 
when the operator is not in constant attendance at the Switchboard; or 
at night when the operator has retired, the bell can be placed adjacent 
to the bed and when a drop on the Switchboard falls, the operator will 
be awakened by the bell ringing. In the day time if the operator is con¬ 
stantly at the Switchboard, the ringing of the night bell is annoying yet, 
in some cases it is not desirable to dispense with some warning signal. 
By using the pilot lamp, the use of the night bell in the day time is obvi¬ 
ated, the pilot lamp affording a very conspicuous signal which cannot be 
ignored. This arrangement is shown in Fig. 170, from which it will 
be seen that when the relay is operated, instead of the bell ringing, the 
current will be directed through the lamp which will remain lighted until 
the operator restores the drop, thereby de-energizing the relay, and put¬ 
ting out the lamp. It is customary to use a white or opal lamp cap for 











































MAGNETO SWITCHBOARDS 


110 


the line drop pilot, and a red lamp cap for the lamp connected to the 
clear-out drops. 

A half ampere fuse is placed in the circuit, and a battery of 8 ordi¬ 
nary dry cells may be used. These will last from 6 to 12 months. Some¬ 
times this fuse is blown or accidentally broken, and the circuit fails to 
operate. Aside from this very little trouble occurs. A switching key 
to control the lamps and night bell is wired in the circuit as shown. 

The line and night bell circuit constitute what may be termed the 
calling circuit of the Switchboard, and the next circuit to be considered 
is the cords by which the calls are answered and the different lines con¬ 
nected together. 



PILOT LIMP 4 RELAY CIRCUIT*; 

Fig. 170. 


Referring to Fig. 171, two telephones are shown connected to their 
respective jacks, the drops being omitted as they are out of circuit when 
the plugs are inserted, while between the two jacks is shown an ordinary 
cord circuit. It will be seen that the lines are connected together by the 
heavy lines, which represent -the cords, the clear-out drop being bridged 
directly across the circuit. Owing to the high impedance of the drop it 
has very little if any effect upon the voice currents which pass from tele¬ 
phone to telephone exactly the same as if the two instruments were con¬ 
nected by a pair of wires instead of the cord circuit. 



TJrUerpnONfir 
I TALKING 


&&£ a * e>e 

Tfc-i_ePK-VO^E: 
TAi_K|No CJPiCOIT 


Fig. 171. 

Fig. 172 shows the operator in the act of ringing a subscriber; note 
how the key cuts off one plug so that ringing currents will not affect the 
































































120 


TELEPHONOLOGY 


waiting ’phone. When the handle o p ringing key is released the circuit 
is completed from one plug to the other. 



Fig. 172. 

Fig. 173 shows the operator in the act of listening and when the key 
is pressed, the springs move outwardly, and the operator’s telephone is 
connected in circuit. This key is so constructed that when moved into 
the listening position it will remain there, and this enables the operator 
to converse with the parties connected, or only one of them, if only one 
cord of the pair is in use. 



Fig. 173. 


In case it is necessary to ring with both plugs, a ring back key is 
connected in circuit, which operates in the same manner as the key previ¬ 
ously described. 

There are various forms of ringing and listening keys. When it is 
necessary to ring with only plug, a key like the one shown in Fig. 174 is 
used. If the key is thrown in a listening position it will stay there owing 
to the shape of the springs, while if pulled in the opposite direction, it 
will fly back to normal when released, thus completing the circuit from 
one plug to the other. 

When it is necessary to ring with both plugs, the key of the tyoe 
shown in Fig. 175 is used, which is the same as the key previously 
described, except that an additional set of springs and handle for ringing 
on the other plug is provided. 

The clear-out drops are usually wound to 500 Otms, and are of the 
armored type in which the coil is inclosed in a tube or shell. This is abso¬ 
lutely essential, for, as the drops are mounted s^de by side if the shell is 
not present cross talk will occur between adjacent coils when two circuits 
are in use. 

The clear-out drop should be very sensitive, as in “ringing off” a 
subscriber only gives a short turn of the crank, and furthermore, as there 







































































MAGNETO SWITCHBOARDS 


121 


are usually two telephones connected to the cord circuit, the clear-out 
drop is, to a certain extent, short circuited by the ringer of one of the 
telephones. This is shown by Fig. 176, where subscriber “A” is shown 
in the act of ringing off. At subscriber “B”, the receiver is shown on the 
hook, and the ringer is therefore across the line. Now if this ringer is of 
80 Ohms resistance, which is commonly the case with these instruments, it 



Fig. 174. Fig. 175. 


will be seen that all the current ^rom subscriber “A’s” generator will 
traverse the line and ring the bell at “B’s” telephone, while the clear-out 
drop, owing to its high winding, will get but little of the current. It there¬ 
fore becomes necessary to do one of two things, either to decrease the re¬ 
sistance of the clear-out drop, or increase the resistance of the telephone : 
ringers. It is a bad practice to decrease the resistance of the clear-out 
drop, for in this case when two parties are talking, some of the voice • 
currents would leak through the drop, which does not occur when it is 
high wound. It is therefore better to use high wound ringers in the 
telephones, and it may be said that ringers o'' less than 250 Ohms resist¬ 
ance should not be used in telephones for local exchange work. 



In order to adapt cord circuits of the average magneto switchboard 
to selective party line signaling so that no interference will take place, 
especially so that the act of calling the exchange or of ringing-off by 
either of the connected subcribers will not cause the bells of the selective 
subscribers to ring or even tap, some special arrangement is necessary. 
This defect is present in nearly all party-line systems when regular 
cord circuits are used. 
























122 


TELEPHONOLOGY 


In addition to this a great many party-lines are of sufficiently high 
resistance between the exchange and the location of the telephones so 
that the shunting effect of the low wound drop winding at the exchange 
to the ringing current is not enough to prevent some of the ringers con¬ 
nected to the same line from tapping or even ringing. This question of 
doubtful operation led one of the prominent manufacturers to perfect 
a special magneto cord circuit, as shown in Fig. 177, which prevents 
parties when ringing off, causing the telephones on the connected party- 
line from ringing. 

It will be seen that this circuit differs only from the standard bridged 
clearing-out drop circuit in that two condensers, “A” and “B” are con¬ 
nected in series between the tips and sleeves of the plugs. 



COA1DEN5ER.. 

CONDENSER. XYPE- 
COR.O C-lP-OUlT- 


RlNOlNo OFF-. 


CONNECTED PARTY LINE 
WITH SELECTIVE- RlNoeR.S>, 


Fig. 177. 


The novelty of this circuit is the connection of the high wound clear¬ 
ing-out drop “c” diagonally across the cord circuit so that one condenser 
is in series with same for the ringing-off current from either connected 
subscriber; also that the two condensers are in series to any current which 
would pass through the party line ringers “d”, “e”, “f” and “g” of a con¬ 
nected line and cause the latter to false signal. The fact that the appar¬ 
ent resistance of the two condensers in series is very high for the low fre¬ 
quency ringing currents, and of low resistance for the high frequency 
voice currents gives the desired result in both cases. The installation 
of the condensers in the manner desired does not materially affect trans¬ 
mission, and the method of installing the condensers and clearing out 
drop in the cord circuit enables same to be used like any other cord. 
Thus, it is not necessary to put one special plug of each pair into the jack 
of the party line when making a connection. 

This cord circuit also possesses an advantage over the regular type 
of cord circuit that a low wound series telephone on a short line will not 
prevent the clearing-out drops from operating, or the accidental short 
circuit of one of the connected lines will not tie up the line connected to 
the other side of the cord. 

Another circuit arrangement for accomplishing the latter purpose, 
is shown in Fig. 178. 

The 1,000 Ohm drop and 2 M. F. condenser are arranged as shown. 
When either subscriber “rings-off” the current divides between the drop 
and condenser. The frequency of the ringing current is so low that the 
condenser offers a high resistance to the current, thus causing it to flow 
through the drop, operating same. With this plan, Phones “A” and “B” 
may be both series or Bridging, or one of each. 

































MAGNETO SWITCHBOARDS 


123 


Another circuit is shown in Fig. 179, which has the advantage of a 
bridged clear-out drop. Here two non-inductive coils “N” “N,” are 
placed in series between the tips and sleeves of the cords as shown, with 
the drop “D” connected at the center points. Assume that “A” and “B” 
are connected as in Fig. 178. When the ring-off takes place, the current 
from station “A”, for example, passes to the center point of non-inductive 
coils “N” and “N”, whence it finds two paths, one through the ring-off 
drop “D”, and the other through the telephone “B”, via the other halves 
of coils N and N. Since the two halves of these coils equal 500 ohms re¬ 
sistance, it is immaterial as to what the resistance of telephone “B” is; 
hence, as in the other case, the telephones may be alike or different. Should 
the disconnecting current originate at telephone “B”, the operation would 
be reversed, obtaining the same results. Cords so equipped should not be 
used for connection from “Toll to toll,” as it increases the static capacity. 
No harm results from their use for “Local to toll.” 




The Monarch Tel. Mfg. Co., have recently introduced a cord circuit to 
accomplish the same result as the circuits just described, which uses a 
combination of clear-out drops and lamps, as shown in Fig. 179a. 

The two plugs are separated by condensers. The two clear-out drops 
are bridged on each side of the cord. A ring off signal received on one 
side of the circuit will not pass through the condensers, but will operate 
the clear-out drop. The condensers do not interfere with the passage of 
the talking currents, which pass from one plug to the other in the usual 
manner. 





































































































124 


TELEPHONOLOGY 


The lamps are so connected that upon the clear-out drops falling, the 
lamps will be lighted, thus affording an additional signal to the operator. 
This circuit practically assures double supervision on a magneto board, 
and is unique in this respect. 

The actual arrangement of the cord circuits in the usual magneto 
board is shown in Fig. 180. This shows the calling and answering plugs, 
their location on the face of the switchboard, and the ringing and listen¬ 
ing and ring-back keys. The theory of this circuit is shown in the upper 
corner of Fig. 180. 




Fig. 181 


Fig. 180 


The most common trouble with cord circuits is due to defective cords. 
It is surprising that the majority of small exchanges do not pay more 
attention to testing their cords regularly. Cord trouble may be sus¬ 
pected, when a scraping, scratching noise is heard, and when at times it 
is impossible for subscribers to hear each other when connected. The 
location of this trouble is usually easy. Any jack in the switchboard 
should be connected to two cells of battery, as shown on left hand side 
of Fig. 181. 

The plug and cord to be tested should be inserted in this jack and 
the listening key thrown exactly the same as when answering a call. The 
cord should then be violently shaken, pinched and bent in all directions, 
especially at the handle of the plug where the trouble usually occurs. If 
there is the slightest “cut-out” or break in the cord, a loud scraping and 
scratching noise will be heard every time the loose connection is dis¬ 
turbed. 

It is easy to tell when a cord is short circuited. Simply throw the 
ringing key without putting the plug in any jack and turn generator. 
If the buzzer which is usually connected in circuit with the generator, 
operates, the cord is short circuited. 

Several forms of cords are in use, the two prevailing types being 
composed of tinsel, or solid wire conductors coiled in spiral form, as 
shown in Fig. 182. 


















































MAGNETO SWITCHBOARDS 


125 


CT ^ivo^ eCen i Y 4 - there ^ Wa f. , pla 9 ed on the market a cord composed of two 
P a oificf' uc , tors of ®° Ild wi r e of special composition, which has proven 
hpfnrf if fa ^° r i y ' . When a tmsel cord breaks, it causes a scraping noise 
• Iwf entirely gives away, whereas, the spiral cord breaks clean, and 

fhp fine i° re this objection. It is also necessary when using 

the tinsel cord to form up the ends where they are connected to the plug 
and wrap the same with wire or thread, whereas with the spiral cord 



Fig. 182. 



DRAW UP ENO 

W them pull 
IT UNDER THE 
WINDING BY 

eno "y_ 


SLEEVE CONNECTION. --TIP CONNECTION. 



c ReMOVABLe SLEEVE COVER. 



A SECOND 
METHOD FOR. 
R.EPAIR.ING 
CORDS BY 
BlNOlNG OUTER. 
BRAIDING AG 
PER METKOO 
SHOWN IN FIGS. 
o,e AND F. 


Fig. 183. 


the conductors are simply pulled out and bared and the ends connected. 
The temper can be taken out of the spiral conductors by putting them in 
a match flame for a few seconds. 

The plug end of the cord is the first to show wear and become defec¬ 
tive, due to continued handling by the operator, the remainder of the 
cord seldom causing trouble. A reinforcement is braided into this part 
of the cord as an extra protection and is made 18" long so that by care¬ 
fully butting the cord each time it becomes defective, it is possible to make 
as many as seven plug-end repairs. 

In making a cord repair its covering is cut back a sufficient distance 
to remove the defect. The latter is located by using the cord test jack 
as previously described. The raw edge of the outer braid is now folded 
under or pushed back, as shown at “B” in Fig. 183, using a small screw 
driver for tucking the braid under. This makes an enlarged portion at 
the end of the cord which will tightly screw into the thread of the plug. 
The covering of the exposed sleeve conductor (provided with colored 
insulation) is now cut away, leaving it entirely bare while the tip conduc¬ 
tor is bared to proper length to go under its binding screw when inserted 















126 


TELEPHONOLOGY 


in the plug, or to receive a tip which later should be soldered to the cord 
conductor. It is also good practice to bind the raw edge of the braiding 
of this tip conductor as shown in “D”, “E” and “F”, Fig. 183. 

The sleeve conductor is doubled back when the cord is screwed into 
the plug so as to make a good contact with the metal body of the latter, 
care being taken that the cord makes a tight fit. The projecting ends 
of the sleeve conductor is now cut off flush with the plug body and the 
tip conductor securely fastened by the clamping screw. 

A cord without beeswax filling may be repaired by wrapping with 
stout beeswaxed linen thread instead of tucking the outside braiding. 
This is a good method of butting, the binding operation being as shown in 
the last two views of Fig. 183. 



The necessity and importance of testing cords regularly, at least 
once a week, in exchanges no matter how small, cannot be too strongly 
emphasized. Considering the ease with which cord test jacks can be 
rigged up, there is no excuse for neglecting this point so vital to good 
service. 

Aside from defect in cords, very little trouble arises in cord circuits. 
An occasional bad contact will be found in the keys, but it may be said 
that this seldom occurs, and unless thoroughly familiar with adjusting 
keys, it is better to leave them alone, or get some one familiar with the 
equipment to make the necessary adjustment. 

Occasionally a clear-out drop fails to operate, in which case the drop 
winding will probably be found open or short circuited. This can be 
located in the same manner as an open drop winding, by plugging into 
a jack connected to a test phone. If upon ringing the generator turns 
hard, the clear-out drop is probably short. If the generator turns easily, 
the winding may be open and this can be determined by using a receiver 
as previously described. 

The cord circuits here described are the standard forms generally 
in use. Each manufacturer has his own method of cabling the different 


















































MAGNETO SWITCHBOARDS 


127 


wires and arranging the various portions of the equipment, but in prin¬ 
ciple, the various switchboards differ but little from each other. 

The operation of the ringing key has been described, and the appara¬ 
tus necessary for ringing is shown in Fig. 184. 

Here it will be seen that the wires from the generator with which 
the switchboard is equipped, are connected to key known as the “Genera¬ 
tor switching key.” When this key is in its normal position the 
hand generator is connected in series with the buzzer and with C and D, 
which in turn are connected to the outside springs of the ringing keys 
as shown in Fig. 180, C being the sleeve side, D the tip. When the gener¬ 
ator switching key is turned down, the hand generator is disconnected, 
and the power generator is connected in circuit. A power generator is 
adapted to be driven by water or an electric motor, or some other source 
of power, and may be located some distance from the exchange and the 
current can be brought into the exchange over wires which are connected 
to the terminals in the back of the board. In place of a power generator, 
a pole changer can be used, and will be found most satisfactory for small 
or medium size exchanges. 

The buzzer used in the generator circuit should be wound to a resis¬ 
tance of 80 to 250 ohms. The use of a higher winding should be avoided 
as it will not allow sufficient current to pass for ringing on heavily loaded 
lines. 

It will be noticed by reference to Fig. 184 that a lamp is inserted in 
one wire leading from the power generator to the switchboard. This 
is an ordinary 16 candle power lamp, and is used to prevent short circuit¬ 
ing the generator when ringing on a short circuited line, which, if the 
lamp was not used, might damage the power generator or pole changer. 

If the generator circuit fails to operate, the fingers should be placed 
directly across the outside springs of the ringing keys. If no current 
can be felt here, place the fingers across the terminals where the wires 
connect to the generator, and turn the crank. If no current is felt at 
this point, the trouble is in the armature winding. 

In case it is impossible to ring from the switchboard, before decid¬ 
ing that the trouble is in the generator circuit, all the plugs in the switch¬ 
board should be tried. If one will ring 0. K., the trouble is not in the 
generator circuit, but is somewhere in the generator wires leading from 
key to key. If, however, none of the plugs will ring, it is reasonable to 
suppose that the trouble is in the generator circuit itsel \ If it is possi¬ 
ble to ring with the hand generator and not the power, it is evident that 
the trouble is in the power circuit. The fingers should be placed across 
the terminals in the rear of the switchboard to which the power wires 
are connected. If current can be felt at this point, examine the contacts 
of the generator switching key and wiring thereto. 

It may be found that neither the hand nor power generator will 
work, and it may happen that the buzzer is open. To test for this, short 
circuit the terminals of the buzzer with a piece of wire, and see if it is 
possible to ring with the plugs. If it is, the buzzer coils should be re¬ 
wound. 

The hand generator for switchboard work should be of the heavy 5 
bar type, and it is well to teach the operator to turn the hand generator 
steadily, and when ringing signals on country lines, to throw the ringing 
key the proper number of times. This is better than ringing signals 
by turning the crank, as this destroys the teeth in the gear wheels owing 
to the sudden jerks. 


128 


TELEPHONOLOGY 


It is customary in the better type of switchboards to mount the gener¬ 
ator in the back of the board where it is accessible for examination with¬ 
out disturbing the operator. In older boards the generator is located 
directly under the key shelf where it is in the way of the operator’s 
knees, and the gear wheels catch the clothing. Sometimes it was located 
inside the key shelf, and to examine it, it is necessary to disturb the oper¬ 
ator and interfere with the service. It should therefore be specified 
that the generator be mounted in the rear of the cabinet. When this is 
done the shaft connecting the crank with the generator should be pro¬ 
vided with a flexible joint so that in case the front bearing gets out of 
line, no strain will be thrown on the gear wheels. A couple of drops 
of oil should be applied to the generator bearings occcasionally, taking 
care not to use too much. Occasionally the contact between the armature 
pin and spring should be cleaned and the contact examined to see that it 
is not wearing to an undue extent. 

When the same power generator or pole changer is connected with 
two or more sections of switchboard, particular care should be taken to 
connect the same side of the power generator to the same side of the cord 
circuits. By referring to Fig. 180 it will be seen that the C side of the 
generator circuit connects to the sleeve side of the plugs when the ringing 
keys are thrown. Therefore the same side of the power generator should 
go to all the sleeve terminals of the power generator circuits in the various 
sections of the switchboard. It is also well to use separate lamps in series 
with this side of the circuit to each operator’s position. 

If two positions of the switchboard are connected up in opposite di¬ 
rections, and two operators should happen to ring on grounded lines at 
the same time, they would not only fail to ring, but would short circuit 
the power generator. Particular care should therefore be taken to con¬ 
nect power generator or pole changer properly. 

It soon becomes evident in an exchange of any size, that some auto¬ 
matic source of ringing power is necessary, as the work of constantly 
turning the hand generator is considerable. 

While generators driven by power are almost exclusively used in 
large exchanges, the cost is prohibitive to the small exchanges. This 
is due to the fact that current is only required at intervals, while the 
machine runs all the time and the cost of power to drive same is quite 
expensive. 

By using batteries, power is only used while actually in the act of 
ringing; but as a battery current is direct, or in one direction, and alter¬ 
nating current is required to ring a telephone bell, some device is neces¬ 
sary to change the direct current to alternating. 

A pole changer is a device for this purpose and changes the direct 
current from a number of cells (usually dry cells) arranged in series 
to give sufficient voltage, into a current alternating in character which is 
suitable for ringing purposes. 

This apparatus consists of an electro-magnet similar to the magnets 
in an ordinary electric bell, in front of which is mounted an armature 
carrying a pair of contacts. The electro-magnet is usually operated by 
a cell of closed circuit battery (dry batteries won’t do) and when in oper¬ 
ation the armature carrying the contacts vibrates to and fro, same as the 
armature and clapper of an ordinary bell. 


MAGNETO SWITCHBOARDS 


129 


The contacts are so arranged that they connect each line leading to 
the ringing keys in the switchboard, first to one side of the battery and 
then the other. Thus it will be seen that the direct current is changed 
at every swing of the armature. This action will be clearly understood 
by reference to figure 185. 

The moving contacts are marked -f- and —. The vibrator coils are 
shown connected to the closed circuit battery. Now imagine the moving 
contacts to be thrown to the right. By tracing the circuit, it will be seen 
that the current from the + side of the 50 open circuit batteries flows 
through the D. P. switch and out through the + moving contact to the 
left hand ± terminal, while the — side of the battery flows to the right 
hand ± terminal in the same manner except that it passes through the 
relay winding shown in the upper right hand corner. The function of 
this relay will be explained later. 


DIAGRAM No4 
Warner Ringing Machine 

FOR. 

Act Alternating Ringing 



Fig. 185. 


Now when the vibrating contacts move to the left, this process is 
reversed and -f- current is connected to the right ± terminal and —‘ 
current to the left. Thus a current alternating in character is produced 
and will continue as long as the vibrator continues to work. It will be 
observed that as long as nothing is connected to the ± posts, no cuiient 
will be consumed from the dry cells, the machine being operated entirely 
by the single closed circuit cell, which lasts for six or eight months, it 
can then be renewed as follows: 

To Make Solution .—Fill the jar with water to line on the inside. 
Then open the can of granulated potash by cutting out the bottom 
(which is made of very thin tin) with a pen-knife. Add the 
potash gradually to the water, stirring the solution constantly, until the 
potash is entirely dissolved, which will take about three minutes. When 
the solution cools it may be found necessary to add a little more water 
to bring it up to the brown line again. Then pour a layer of heavy 
Paraffin oil (from the bottle furnished) on the solution in the jar, until 

9 . 














































130 


TELEPHONOLOGY 


it covers the blue line. In stirring the liquid avoid splashing it. The 
potash will burn the skin and clothes. 

Unless a short circuit should occur, the battery requires no attention 
until it is exhausted. A short circuit between the plates in the cell or 
a short circuit outside will destroy the whole battery. 

When the cells become exhausted the solution and the remains of 
the zinc and oxide plates must be thrown away. All the remaining 
parts can be used again. 

To take the cells apart, lift the lids, unscrew the bolts, and remove 
the zinc and oxide plates. Wash off (with water) the copper frames, 
bolts and rubber insulators, brightening up the metal where corroded, 
with emery paper, especially the inside grooves of the copper frame 
sides. Pour away the solution carefully and set up cells with new potash, 
oxide plates and zinc according to directions. 

In taking the cells apart, the parts that have been immersed in 
potash must be washed before they are handled. 

To ascertain if the oxide plates are exhausted, pick into the body 
of the oxide plates with a sharp pointed knife. If they are red through¬ 
out the entire mass they are completely exhausted and need renewing. 
If, on the contrary, there is a layer of black in the interior of the plate, 
there is still some life left, the amount being dependent entirely upon the 
thickness of the layer of black oxide still remaining. 





Jm 


"n Poi ' t ft 


cu>«# 




pay Ceus t 

C / A . 

3AZ 



?=$><? 

- |i|i!i|i|i|i|i|i|J 



L -* To Sn-ao 


Fig. 186. 

Too great stress cannot be laid on the necessity of observing, when 
setting up the cells, that the top of the oxide plate is fully one inch below 
the surface of the potash; and consequently about 11/2 inches below the 
top of the oil. 

The difference of one inch in the height of the solution in the jars 
determines the success or failure of these batteries. 

The machine is set up and wires from the closed circuit battery con¬ 
nected as shown in Figure 186. 

The parts are usually tagged to denote the proper connections. The 
closed circuit battery should be as close to the machine as possible and 
connected with not less than 16 copper wire. The dry cells can be loca¬ 
ted at any convenient place, from 40 to 60 cells being used. These are 
connected in series, the zinc of one going to the carbon of the next, the 
last carbon and zinc going to the machine. Each dry cell gives IV 2 volts. 

For local work where the lines are not heavily loaded or long, 60 
volts is sufficient. The more ’phones on the lines, the more batteries 
required. Make the battery strong enough to ring the most distant 
’phone and the short lines can take care of themselves. 

After setting up the battery and closing switch on the machine, the 
vibrator should start, if not examine the contact point “E”, figure 186a. 
Start the vibrator gently with the fingers; make sure the closed circuit 















MAGNETO SWITCHBOARDS 


131 


battery is 0. K., and properly connected. When the contacts V and W. 
are in contact with B & D, brushes A and C should be about one-eighth 
of an inch away from the vibrator contacts on that side and vice versa. 

The function of the relay shown at M, in the figure is to 
prevent the sparking at the contacts A, B, C, D, by conecting the conden¬ 
ser, which is located in the base of the instrument, across the lines where- 
ever the pole changer is used. 

If the condenser were permanently connected across the ringing 
wires, the alternating current would constantly flow through same and 
the batteries would suffer. 

The figure shows the Pole Changer in detail. The letters denote 
the different parts, the names of which are as follows: 0 P. Q. M. N. 
K. and L. constitute the condenser relay. 0 is an adjustable weight. 
P is an adjustable post for regulating the throw of armature N. Q is the 
T shaped frame of the relay. M is the actuating magnet. K is a con¬ 
tact spring, and L is a contact post. 



Fig. 186a. 

The operation of the relay is as follows: When no current is being 
drawn from the batteries the armature N. is resting on the adjustable 
post P and the contact spring K is lifted clear off the contact post L. 
Now, when the operator signals a subscriber the current is brought 
through the magnet M which instantly draws down the armature N and 
closes the condenser circuit through the contacts K and L. Thus the 
condenser is automatically connected across the ringing circuit each time 
the operator signals a subscriber, and is disconnected in the same man¬ 
ner. 

The letters I, R, E, F, H, T, show the principal parts of the vibrator 
mechanism. I is the electro magnet, and is energized by the current 
from the single closed battery. This immediately draws the armature 
R toward the magnet until the circuit is opened at the contact E; then 
the spring, which supports the armature R and the vibrator tongue H, 
bring the armature back until the circuit is closed at the contact E; then 
the magnet again attracts the armature and the operation is repeated 






















































132 


TELEPHONOLOGY 


over and over. It will, therefore, be noted that the operation of the 
vibrator is as simple as an ordinary door bell. The weight 0 should be 
adjusted together with the screw P, until the contact K is only about 
1-64 inch away from L. This contact should close every time the machine 
is used and should open again immediately when the current ceases to 
flow. 

The wires to switchboard are to be run in a most convenient man¬ 
ner. It is convenient, however, to have a buzzer in the power circuit, 
and if only one board or section is to be supplied with power then the 
buzzer may be placed anywhere in the power circuit. But if more than 
one board or section is to be supplied with power, then a buzzer should 
be supplied for each board, and should be connected as shown in Fig. 
187. 



Usually switchboards are arranged with a generator switching key 
already wired in circuit and terminals are provided to which the power 
generator or pole changer can be connected. This is shown in Figure 
184 and it is simply necessary to connect the wires from the pole changer 
to terminals 6 and 7 as shown in illustration, or other terminals marked 
for the generator. When more than one section of board is used, it is 
absolutely necessary to connect the same side of pole changer to the same 
terminal in each section. That is, connect all the No. 6 terminals to one 
side pole changer circuit and all 7 terminals to other side. In series with 
wire to each No. 6 terminal place an ordinary incandescent lamp, as 
shown. 

The pole changer shown in figure 186a is also arranged to give pul¬ 
sating direct current for ringing biased bells used in connection with 
selective telephones. In operation and construction this instrument is 
the same as the one previously described except that two additional bind¬ 
ing posts are provided for the + and — pulsating current. Figure 188 
shows these extra posts, which connect to the switchboard as shown in 
Fig. 245, the ground post being connected to terminal 17, as shown in the 
figure (245.) 

In place of the large number of dry cells necessary with the pole 
changer any source or direct current, such as the ordinary incandescent 
light circuit not exceeding 110 volts may be used. It is necessary to 
connect one or more lamps in multiple as shown in figure 189. 

To prevent an excessive amount of current from entering and injur¬ 
ing the machine, try one lamp and if this does not ring properly, more 
current is necessary and another lamp can be used connected as shown. 




















MAGNETO SWITCHBOARDS 


133 


Great care must be taken when this method is used to prevent the con¬ 
tacts from sparking. For light ringing this will give satisfaction. 

♦Experience has shown that a pole changer is an exceedingly desira¬ 
ble and economical device for the small exchange, whose small size is 
hardly sufficient to warrant the necessary expenditure for the electrical 
machinery required in the installation of a ringing dynamo. There are 
very many instances, particularly as the small exchange increases its 


Diagram N®5. 

w#rner Ringing Macmi^c 

ALTERNATING andPULSATING ringing. aroun* 



capacity, when it is practicable for the wire chief to construct a pole 
changer out of materials at his hand, and thus avoid the expense of pur¬ 
chasing a machine outright. So, the object of this article is to describe 
a method that has been successfully put into practice for accomplishing 
this result. 



Fig. 189. 


The materials required are : A board for a base, 5" X 9"; one 
3" gong iron box vibrating bell; one 1/2 M. F. condenser; one single con¬ 
tact relay of not over 80 ohms resistance; six brass binding posts, such 
as may be taken from old dry batteries; eight platinum hookswitch 
points; four strips of brass, % X 1 Vi"J six inches of light watch spring; 
a few screws, etc. The bell should be prepared by cutting the frame at 
the edge of the gong and cutting the hammer rod so as to leave 1 / 2 " of 
stub. To this stub solder a piece of No. 12 iron wire 4" long, which has 
been flattened slightly. 


* American Telephone Journal. 


























































134 


TELEPHONOLOGY 


Slip over the wire a piece of hard wood 3" X %" X Vs" which has 
two 3-32" holes apart, as shown at e. It may be well not to dress 
the wood down to dimensions until after it is bored and in place. Place 
in the two holes two contact pins, made by cutting off the heads of two 
binding posts and soldering to each end of both platinum points. Place 
some sort of a light weight on the end of the vibrator, with which to 
govern the rapidity of its vibration, which should be about twenty com¬ 
plete vibrations per second. 

Screw the vibrator to the base, which has been smoothed and var¬ 
nished, and so adjust it that the points shall be one inch from the base. 
Cut four pieces of brass, as shown at a, and solder to them pieces of 
spring, as at c, and bend together, as at b. Bend the spring so it will 
have only a slight tension against the brass. It will be necessary to 
draw the temper in the springs, as they are too brittle without. Care¬ 
fully punch the holes for the platinum points and solder them in on the 
back, as the springs will not bear much riveting. 

Screw these contact brushes to the base so that the points on the 
pins will strike the points in the springs quite firmly when the vibrator 
is run with one cell of dry battery. Be sure that both contacts on one 
side make and break at exactly the same time. 



Fig. 190. 


Mount the relay in the most convenient manner and make all connec¬ 
tions, as shown at e. Connection to the contact pins should be made by 
means of wires brought to the end of the vibrator tongue and connected 
to posts driven in the base, by flexible cords or coils of wire, as is plainly 
shown in Fig. 190. The terminals are mounted on the bottom of the base 
and the machine raised on short legs or the connections brought out to 
binding posts. The machine will work much better if held firmly and not 
allowed to vibrate as a whole. 

While this machine may appear crude in comparison with the pur¬ 
chased article, when carefully made it will give very little trouble and 
requires no attention. 

A very good substitute for a relay may be made from an old drop by 
soldering on a piece o c brass for a contact and a binding post for a coun¬ 
terbalance. Or even the windings of an 80-ohm bell may be made to serve. 

The next portion of the switchboard to be considered is the Opera¬ 
tor’s telephone or “set.” The usual form of operator’s set is wired as 

































































MAGNETO SWITCHBOARDS 


135 


shown in Fig. 191. It is commonly the practice to use three cells of blue- 
stone battery for small switchboards. Dry batteries should never be 
used for boards in constant service, as they soon become worthless. The 
bluestone battery is not ideal for this service, but as they deliver a small 
but constant current and are cheap to install and renew, they are used 
to a considerable extent. 

By tracing the circuit, it will be observed that the transmitter and 
primary of the induction coil are in series with the battery when the 
plug connected with the head receiver is inserted into the jack, which is 
located in the front of the key table. The inner contacts of the jack are 
placed in series with the battery and transmitter in such a manner that 
the battery circuit is open when the plug is withdrawn from the jack, 
which saves the battery when the board is not in use. 



The secondary winding of the induction coil is in series with the 
operator’s head receiver, and terminals “A”, “B”, which connect with 
the sleeve and tip sides respectively of the cord circuit listening keys 
shown in Fig. 180 and 193. 

When a breast transmitter is used the circuit is as shown in Fig. 
192, and a plug with 4 or 5 contacts is used. 

Each strand of the cord has different color insulation and should be 
connected as shown. In renewing cords it is important to see that the 
cord is properly connected. 

The secondary of the operator’s induction coil is usually wound to 
a higher resistance than coils used in telephones. This is to prevent the 
cord circuit from being short circuited when the operator “listens in” 
on the same. The usual resistance is 100 to 250 ohms. 

Many different types of coils are used. Some manufacturers use 
coils of special design with large cores and winding space, so as to secure 
powerful transmission. 

The operator’s circuit is very simple. It is easy to trace the primary 
circuit from the battery to the transmitter through the primary and jack 
contacts, back to the battery circuit, while the secondary winding of the 
coil is in series with the operator’s head receiver, and the listening con- 
































































































136 


TELEPHONOLOGY 


tacts of the keys in the cord circuits. By referring to Fig. 180 it will 
be seen that when any key is thrown, the secondary winding of the opera¬ 
tor’s induction coil and the receiver are bridged directly across the cord 
circuit. 




Fig. 193. 


The troubles met with in this circuit are few, usually consisting of 
broken transmitter or receiver cords. If the operator can hear the sub¬ 
scribers but the subscribers cannot hear the operator, the trouble is either 
due to a short circuited secondary in the induction coil, or to a defective 
transmitter or broken cord leading thereto, or the batteries are in bad 
condition. When this trouble occurs, first test the battery by removing 
wire from terminals in rear of board, and connecting to these terminals 
two cells of dry battery. If this cures the trouble, it will be apparent 
that the trouble is in the bluestone cells and they should be re-charged 
as described in the chapter dealing with batteries. If this is not the case, 
connect an ordinary series telephone to the terminals of the operator’s 
set and push the operator’s receiver plug into the jack. See that the 
contacts in the jack close, and if so, turn the crank on the telephone or 
test set. See if the circuit is complete which will be donoted by the bell 
ringing. If the circuit is not complete, the transmitter cords should be 
carefully examined and it will probably be found that one is broken. If 
this is not the case, short circuit the primary of the induction coil, and 
if the circuit then tests all right, the trouble is an open primary, and a 
new coil should be substituted. 

It should be remembered in making the following tests to have one 
of the listening keys thrown in a listening position, with one of the plugs 
connected with that pair of cords short circuited by wrapping a piece of 
wire around the sleeve and tip. 

If the operator cannot hear the subcribers, the first thing to exam¬ 
ine is the receiver cord. It is usually better to substitute a new cord. 
Then with the listening key thrown and plug short circuited as above 
described, short circuit terminals A, B, or short circuit the wires run¬ 
ning from the operator’s set to the keys. If by talking into the opera¬ 
tor’s transmitter, the set tests all right, the trouble lies between the point 
















































































MAGNETO SWITCHBOARDS 


137 


short circuited and the next key, but if the set will not talk, look for a 
short circuit in the induction coil, a broken wire or bad contact between 
the operator’s plug and jack, or between the point short circuited and 
the operator’s set, but not in the keys, as the trouble is not past the point 
short circuited, but between operator’s set and that point. 

The receiver should also be tested by connecting it to an ordinary 
telephone as the winding of same might be open. If the operator com¬ 
plains of hearing a scraping noise when talking to a subscriber, and this 
happens with any cord circuit, it is an indication that there is a loose 
connection in the operator’s circuit, or that the switchboard cords are 
bad. To locate this, either short circuit the terminals A, B, or the wires 
running from the operator’s set to the keys. Jf the scrcatching noise 
disappears, the trouble is not in the operator’s set, but in the cords or 
keys; whereas, if the scratching noise continues, the trouble is in the 
wiring of the operator’s set. 

When the switchboard consists of more than one operator’s position, 
it becomes necessary to provide some means for connecting the positions 
together so that one operator can handle the entire switchboard at night, 
or at other times when necessary. 

This is accomplished by wiring the operator’s set as shown in Fig. 
192a, where it will be seen that a key is provided, which, when thrown, 
will connect two operator’s sets in multiple. By this means, one opera¬ 
tor can use any of the cord circuits of the switchboard at will without 
having to change her receiver plug from one jack to another. 



In addition to the cord circuit shown in Fig. 180, it is sometimes 
customary to wire the cord circuit with only one ringing key. so that all 
calling must be done with the front plug of each pair. This is shown in 
Fig. 193. 

One very important fact to be kept in mind, is that the tip of one 
plug should be connected to the tip of the other. 

A trouble often met with in grounded systems, is that when two 
grounded lines, either of which is all right by itself, are connected to¬ 
gether, they are both “dead”, and canot talk or ring. This can be due to 
connecting up one line to the tip of the jack, while the sleeve is grounded, 
and the other line is connected to the sleeve of the jack, and the tip ground¬ 
ed. By tracing the circuit, which is shown in Fig. 194, it will be seen that 
both lines are short circuited. The remedy for this is to connect up all 
grounded lines one way—i. e., connect all the line wires to the tips of the 
jacks and ground the sleeves. 

A 11 modern switchboards are wired full metallic, and when connect¬ 
ing them up, care should be taken to observe which wire of each pair in 






















138 


TELEPHONOLOGY 


the jack cable goes to sleeve of jack. These wires are usually the ones 
with solid color insulation and should be connected to the ground if 
grounded lines are used. 

Sometimes this trouble is caused by the cords themselves being 
reversed, i. e., the tip of one cord being connected to the sleeve of the 
other, as shown in Fig. 194a. This can be tested for with a bell and 
batteries as shown in Fig. 195. 



Touch one wire on tip of front plug and other wire on tip of back 
plug, and the bell should ring, if not, the cords are probably reversed and 
should be changed. 

By examining the cords, it will be seen that the sleeve or tip con¬ 
ductor has a colored thread running through it, for the purpose of iden¬ 
tification. Some manufacturers place the colored strand in the conduc¬ 
tor to the tip in the plug, while others place it in the sleeve, but in all 
cases, it will be found that all the plugs purchased from any one manu- 



Fig. 195. 


facturer will be connected the same way, with both tips connected to 
the terminals on one side and both sleeves to the terminals on the other. 
If this is not done a great deal of trouble will result, especially where 
grounded or common return wire lines are used. 





































MAGNETO SWITCHBOARDS 


139 


The circuits already described of the operator’s set and line circuits, 
are the standard circuits of the average magneto switchboard, but there 
are many additional circuits, which in a way, may be regarded as special 
but which are necessary in certain cases. For instance, when 2 or 4- 
party selective ringing is used, the cord circuits must be able to perform 
other functions in addition to these already described. 

“*In an exchange where the local lines are grounded and toll or trunk 
lines are metallic, it is often the case that while both the local and toll 
lines are quiet enough by themselves, as soon as a short grounded line 
is connected to a long metallic one the combination becomes so noisy as 
to make it impossible to carry on a conversation over it with any degree 
of satisfaction. This is especially true if there is an arc light circuit in 
town. In such an event it is quite possible that even some of the local 
metallic circuits, if the insulation is low or they run very close to the arc 
light circuit, will begin to hum in a very lively fashion as soon as con¬ 
nected to toll lines. 

To meet such a condition as this it has long been known that the 
proper thing to do is to install a repeating coil in a switchboard cord cir¬ 
cuit, so that the local line need not have any metallic connection to the toll 
line. This will usually cut out the greater part of the noise. Although 
good coils for this purpose can be bought from a number of manufactur¬ 
ers the writer believes that there are still a considerable number of 
telephone men who would like to make such a coil for themselves, and 
put it in their own switchboards. This article will tell some of the points 
which must be looked out for in selecting the material for such a coil, 
and show how to make it easily and cheaply in such a way that a man 
in almost any town can get everything that is put into it at small trouble 
and expense, and fit it together without the use of special machinery. 

Types of coils .—In the first place, a man who is going to build a 
repeating coil has to consider that repeating coils can be roughly divided 
into two classes. Those in one group are designed to repeat both ringing 
and talking currents. Coils of this type can be placed directly between 
two line circuits, and will repeat the “rings” from one line to the other as 
well as the conversation. They are known as “Ring-through” coils. 

Coils of the other type are designed to repeat voice currents only 
These coils are usually wired into the cord circuit of the switchboard in 
such a manner that it is not necessary to ring through them, and are 
known as “Talk-through” coils. 

On making a close examination of successful commercial coils in 
these respective classes, and studying the discoveries which have been 
made in the process of their development one finds that the principal 
variations in construction which will be noticed are: More or less iron 
in core; magnetic circuit open or closed through shell; winding of high 
or low resistance and of heavy or fine wire. 

The amount of iron in the core .—The telephone repeating coil can be 
considered as a form of induction coil. It has two windings upon an iron 
core, both windings usually o ' the same resistance and number of turns, 
so that there is no “step down” nor “step up” effect, such as is usually 
present in other types of transformers or induction coils. It depends 
for its action upon the fact that when currents, alternating in character, 
such as voice or ringing currents, are passed through one of the wind- 


* American Telephone Journal. 





140 


TELEPHONOLOGY 


ings, which may be called the primary, a current is induced in the other 
or secondary winding, which is identical in character with that in the 
primary. Taking up this action in detail, it is found that when a cur¬ 
rent is passed through the primary the core is magnetized. When this 
current decreases, as is the case with all alternating currents which 
change or reverse their induction at every alternation, the energy which 
is stored up in the core in the form of magnetism acts upon the windings, 
and induces a current in the secondary or other winding from the one 
through which the exciting current is passing, similar in all respects, 
except a slight loss in strength and distortion of wave form, to the current 
which produced the magnetism. Some appreciable time is necessary, 
however, for an iron core to be magnetized after current is turned on, 
and for it to give up its magnetism after the current is turned off, or 
when the current is varied in strength the changes in the strength of 
the corresponding magetism do not keep exactly in time with the changes 
in current. The greater the amount of iron, the greater difference does 
one find in this effect. For this reason the amount of iron to be put into 
a core is determined by the class o c current it is necessary to repeat. If 
the coil is of the “Ring-through” type, it must repeat currents having 
a rate of change of about one thousand times a minute and considerable 
Quantity. A large amount of iron is necessary to transform this energy 
with as little loss as possible; that is to say, a large heavy core is neces¬ 
sary when a ringing current of a slow rate of alternations is to be repeat¬ 
ed, so that a considerable portion o ' energy will be absorbed by the core. 
On the other hand, where small weak currents, such as voice currents, are 
passed through a coil with too large a core they are muffled and distorted 
by the slow action of so much iron. The “Ring-through” type of coil is 
therefore not adapted to secure the very best results in repeating voice 
currents only, as without the large core the coil will not repeat ringing 
currents, and with the large core it chokes or muffles the voice currents, 
which have a high rate of change, about 90,000 times a minute, and are 
of exceedingly small quantity, the large iron core being too slow to 
respond magnetically to such rapid changes. 

Open or closed magnetic circuit through shell. —In “Ring-througn” 
coils, the outside shell is connected to the ends of the core, so that a com¬ 
plete magnetic circuit is formed. This adds to the amount of iron sub¬ 
ject to the influence of the windings, and the shell also prevents leakage 
from one coil to another when they are mounted side by side, thus making 
cross-talk impossible. 

In the “Talk-through” type the presence of so much iron is undesir¬ 
able. The core should therefore be separated from the shell, which 
should nevertheless be retained to prevent leakage likely to produce cross¬ 
talk. 

Windings. —The windings of a repeating coil are determined by the 
conditions under which it is to be used. For instance, if the coil is to be 
used for common battery work, the wire must be large enough to carry 
the current without heating. The ohmic resistance is of comparatively 
little importance, as it follows that if a sufficient number of turns are 
put on the coil to properly affect the core, and the wire is of the proper 
size, the ohmic resistance alone is not a factor, except where the coil is 
to be bridged on a line, in which case the resistance is made sufficient to 
prevent any short circuiting effect the coil would have on the telephone 
bells on the line. 


MAGNETO SWITCHBOARDS 


141 


As voice currents are of minute quantity, wire of very small diame¬ 
ter can be used in coils designed to repeat voice currents only. 

The coil to be described in this article belongs to the “Talk-through” 
class, and, owing to its small size and high efficiency, is particularly 
recommended for use in the cord circuits of a switchboard. The exact 
dimensions as given need not be adhered to, in fact, an old induction coil 
spool and the wire from a discarded ringer or generator, will, if properly 
assembled, make an excellent coil. 

Constructing a coil .—To make the spool, take two pieces of wood 
about i/4" thick, and of the proper size to fit inside a piece of iron pipe 
about 2" inside diameter. Bore a hole in the centre of these large 
enough to slip on a tube made by rolling two or three layers of thin paper 
on a lead pencil. After making this tube, the separate layers in which 
should be glued together so that the tube will be quite stiff, glue the heads 
on the tube with 1 1-16” space between heads. These different parts are 
shown in Fig. 196. 



Fig 196. 


One head should be drilled for terminals, which can be made from 
brads or pieces of copper wire, and holes should be made for the wires. 
Lay this out as shown by Fig. 197. Countersink the wire holes on the 
back, as shown in the cross section. 

Get a stick which will fit into the hole in paper tube. Split one end 
of this, and fasten the core on the stick. When in place, drive a wedge 
in the split end of the stick, and the coil will be held firmly. The clear 
end of the stick can be put in a lathe held in the hand. 



Fig. 197. 



The operation of winding the wire on the spool is shown in Fig. 198. 
No. 32 silk covered wire is used. This is the size usually used on 5 bar gen¬ 
erator armatures. The exact size is of little consequence, however. The 
winding begins at terminal No. 1. Run on 1,400 turns, and bring the end 











































142 


TELEPHONOLOGY 


out at No. 2. Then cover with two turns of writing paper. The layers 
should be smooth and firm. The next winding begins at No. 3 and termi¬ 
nates at No. 4. 

Continue until four windings are put on, each winding consisting of 
1,400 turns of wire, with the two layers of paper between each winding. 
A good way to count the turns is to count the turns on one layer, then 
put on the proper number of layers. The wires should be wound on 
evenly in layers, and should be free from kinks or splices, unless the 
splices are soldered and well wrapped. 

When the coil is completed, the outside layer of wire should be cov¬ 
ered with a couple of layers of paper, and the center tube should be filled 
with as many fine iron wires as it is possible to put into it. The fine 
wires from an old induction coil core will answer. Next an ordinary tin 
can of sufficient size to contain the complete coil should be taken. The 
bottom should be drilled with holes large enough to allow the coil termi¬ 
nals to project without touching the tin. 


Fig. 198. Fig. 199. 

A piece of paper should be pasted over each end of the core, so that 
it will not touch the tin can, and the coil should be placed inside the can 
and fastened by two screws, as shown in Fig. 199. Then, if it is desired 
to protect the coil from dampness, the can should be filled with melted 
parafine or beeswax, and the lid soldered on. 

Coils mounted in this fashion can be placed side by side in the switch¬ 
board without danger of cross-talk. When only one coil is to be made, 
the shell can be omitted entirely. 

By turning up two iron heads with shoulders to fit inside the iron 
tube and using two brass bolts to hold heads on tubes, and hold the coil 
firmly in place, a very satisfactory and convenient means of mounting 
the coils is provided. This feature is not found in most ready-made coils, 
which are usually riveted together in such a manner that it is necessary 
to almost destroy the shell to get them apart. 

The next thing is to connect the coil in the cord circuit of the switch¬ 
board, so that it can be used to connect any two lines. 

Fig. 200 shows a circuit which can be applied to any switchboard 
without changing the existing equipment to any great extent. 

Connect the terminals of one cord directly to terminals 1 and 8 of 
the coil. If the switchboard is equipped to ring with one plug only, con¬ 
nect the cord you do not ring with as above. Also connect the clearing 
out drop to terminals 1 and 8. Terminals 2 and 7 of the coil are con¬ 
nected to a V 2 M. F. condenser, which will prevent the passage of ringing 
















MAGNETO SWITCHBOARDS 


143 


currents through the coil, thereby securing the operation of the clearing 
out drop. Terminals 4 and 5 should be connected together. Terminals 
3 and 6 should be connected to the terminals in the switchboard from 
which the cord connected to 1 and 8 on the coil were taken. 

It will be noticed that the clearing out drop will not fall when one 
of the parties connected rings off. When the party connected by means 
of the cord wired to terminals 1 and 8 of the coil rings off, the drop will 
fall, as the condenser opens the repeating coil circuit so far as ringing 
current is concerned, while it offers no opposition to the passage of voice 
currents. The condenser can be omitted when it is not necessary to 
secure the clearing out signal. 



The resistance of the windings of the coil here described are about 
as follows. Of course a difference in the size wire, method of winding, 
etc., will make some change. 


1st winding, or one next to core. 40 ohms 

2nd “ 60 “ 

3rd “ 75 “ 

4th “ 95 “ 


As the 1st and 4th windings are in series when connected, their 
resistance is about 135 ohms. 

The 2nd and 3rd windings are also in series, so that they measure 
135 ohms. 

Each half of the coil consists of 2,800 turns, so that transmission 
is equally good both ways. 

Placing the coil in the cord circuit will not interfere with using the 
cord for regular service, as it would require an expert to determine the 
difference between a cord circuit equipped with a coil of this type, and 
one without it. 

A very good “Ring-through” can be made on the same principle as 
the “talk-through” coil just described, by taking a solid core of soft iron 
3 1-16 in. long, drilled and tapped in each end for an 8 X 32 screw. 



































































144 


TELEPHONOLOGY 


Get three fibre heads 3-32 in. thick, 1 23-32 in. diameter; place one 
directly in the centre of the core, and one on each end. This will give 
two winding spaces, each 1 10-32 in. 

Insulate the core with paper, and wind in each space, 21 layers of 
No. 32 single silk wire, putting a piece of paper between every fourth 
layer. This must be evenly wound. 

When complete, insulate with 2 layers of paper, and wind over this, 
in each space 24 layers of No. 32 single silk-covered wire. 

Connect outside end 0 of inside winding No. 1, to inside end I 2 of 
outside winding No. 2. Terminal I of inside winding No. 1, and O, of 
outside winding No. 2, form the terminal of one side of the coil. 

Connect outside terminal O’ of inside winding No. 2, to terminal I' 
of outside winding No. 1. The remaining terminals form the other side of 
the coil. Each side of the coil is of about 200 ohms resistance. 

The Tube to cover coil consists of a piece of iron pipe o e proper size, 
3 1-16 in. long. The heads are two iron caps or large washers which 
are held in place by the 8 X 32 machine screws going into the core. Care 
should be taken to have the heads fit tightly against the core and 
casing. 

The wires should be brought through bushings in the iron heads, 2 
on each end, and the coil is mounted on a wooden base by cutting a tin 
strap to fit around pipe and fastening same securely so that the coil is 
held firmly in place. 

Care must be taken to have all the windings in the same direction 
and the layers must be smooth. 

This coil gives very good results wherever a ring-through coil can 
be used and will be found comparatively simple to construct; a diagram 
of the connections and dimensions is given in Fig. 201. 


0 - 

/' 

o- 



Another type of ring-through coil is shown in Fig. 201a, which gives 
dimensions of the bobbins. Each bobbin contains about 2500 turns of 
No. 30 single cotton covered wire. The core is made from a bundle of 
soft iron wire No. 24 gauge preferred. The core wires are bent around 
as shown, until they lap, and are bound together with a piece of wire as 
shown. 

This coil may be placed directly in the line circuit as shown in Fig. 
202, the drop circuit being of the usual type where the drop is cut off by 



























































MAGNETO SWITCHBOARDS 


145 


the insertion of the plug. It is better to place the coil in a cord circuit 
as otherwise it is necessary to talk through two coils, should two lines 
so equipped be connected together. Where the coil is put in a cord circuit, 
this cord can be used to connect any two lines. A cord circuit stripped 
of all details except the coil is shown in Fig. 202a. No condenser is need¬ 
ed with this coil. 


/Off: 202. NCPCAUNO CMS IN THC UNC 



fopeartncj Co// 


/Peprafmq Cait 



D=r 7Q 

LJ 




If a grounded line is noisy and is connected to a quiet metallic line 
it will make it noisy also. If the coil is used the quiet line will remain 
quiet. If both lines are noisy the coil will not reduce the noise. 

To insert a “ring-through” coil in a cord circuit, disconnect the ter¬ 
minals of the answering plug from the switchboard, and connect them 
directly to one of the windings of the repeating coil. The other winding 
of the repeating coil is connected with the terminals on the cord shelf 
from which the cord was taken. The resultant circuit is shown in Fig. 
203. 



Here it will be seen that the currents coming in on one plug, will 
circulate through one winding of the cord “R”. The other cord is entire¬ 
ly separated from the in-coming circuit. This keeps each one of the 
10 . 



























































































146 


TELEPHONOLOGY 


plugs in an entirely separate circuit of its own, the only connection being 
the inductive action between the two windings of the coils. 

The “Ring-through” coils for the reasons previously described, do 
not possess the greatest efficiency for talking purposes only, and it is bet¬ 
ter practice to use the smaller “talk-through” coils for switchboard use. 

Sometimes it is desirable to have a cord circuit of the usual variety 
so arranged that by throwing a key, the repeating coil can be cut in. 
This is accomplished by either putting in another key or equipping the 
ring-back key with an additional set of springs, so that when the key is 
thrown, it will remain locked in that position. This circuit is shown in 
Fig. 204, which differs in no way from the cord circuit previously 
described except when the key is not thrown, the cord circuit is regular in 
all respects and when the key is thrown, the repeating coil is cut in. 



Cord circuits equipped with repeating coils are seldom subject to any 
troubles except those met with in ordinary cord circuits. In addition, 
it will be found sometimes that the V 2 M. F. condenser is short circuited. 
When this is the case, it is impossible to throw the clear-out drop. To 
test for this, disconnect one of the wires from the condenser. If the 
clear-out drop will then operate, the trouble is in the condenser. If the 
clear-out drop still refuses to operate the trouble is probably in the clear- 
out drop. If the transmission is bad, the repeating coil may be short- 
circuited. This trouble can only be located by measuring the resistance 
of the various windings. 

In all exchanges where there are some metallic and some grounded 
lines, it is better to equip one or more cord circuits, with a repeating coil, 
and this will be found of material advantage when using 4-party Selec¬ 
tive Ringing with Biased bells, as the cord circuits equipped with the 
repeating coil will prevent the 4-party bell from ringing when the sub¬ 
scriber connected to the other side of the cord circuit rings off. 

The majority of manufacturers will wire the cord circuits on switch¬ 
board for repeating coils, then if it is found necessary, the coils may be 
installed later. This is shown in Fig. 205. 




























































































































MAGNETO SWITCHBOARDS 


147 


By connecting the colored wires to the coil in accordance with the 
small diagram in the upper right hand corner, the repeating coil may be 
installed at any time. The circuit with coil in place is shown in Fig. 200. 

The general care of the switchboard is a point which should be care¬ 
fully considered, and to which very little attention is paid. 

Every day or two, the inside of the board should be blown out. 
Nothing is better for this purpose than a bellows, as this will blow dust 
out of inaccessible corners without damaging the wires. The rack to 
which the cords are connected inside the switchboard should be kept free 
from dust or cross talk will result. The plugs should be regularly 
inspected and kept clean and bright. Occasionally the plugs can be rub¬ 
bed with a little dry pumice stone on a cloth. Don’t use anything that 
will tend to wear the plug or insulation between the tip and sleeve. The 
operator’s transmitter mouthpiece should be kept clean. For sanitary 
reasons if for no other the mouthpiece should be changed occasionally. 
It is well to provide each operator with a separate mouthpiece which 
they can use while on duty at the switchboard. 



Fig. 206. 


Fig. 207. 


The operator should be carefully instructed about putting the plugs 
into the jacks. Do not allow them to drive the plugs in by striking the 
butt of the cord with the palm o p the hand, as nothing will destroy the 
cords quicker. The plugs should be placed in the jacks by grasping them 
by the sleeve, and they should be withdrawn in the same manner. They 
should not be allowed to fall on the key-table, but should be returned to 
their sockets by hand. See if the cords are placed in the Switchboard 
properly, so that they will not cross up and so that the weights will return 
them to their proper position. If the cords are too long, loop them up as 
shown in Fig. 206. 

The batteries for the night bell and operator should never be located 
in the bottom of the Switchboard, but should be placed in a closet where 
they will not be exposed to heat, or some other suitable place where they 
will not be disturbed. 

The selection of proper tools is a matter that should not be over¬ 
looked. Some solder and appliances for heating same should be at hand. 
Resin core solder should be used. This is solder made in the form of 
heavy wire with a hollow center filled with resin. In using this solder it 


























148 


TELEPHONOLOGY 


is simply necessary to apply some to the joint, and the use of acid or 
soldering paste is unnecessary. These substances should be avoided 
around Switchboards as they will cause corrosion and trouble. 

The Switchboard man should provide himself with a long slender 
screw-driver, a pair of needle point plyers, and a pair of diagonal cut¬ 
ting plyers. These, in addition to a head telephone with a six foot cord 
to which is attached a pair of “Frankel” tips, constitute the necessary 
tools for making repairs. 

When soldering a wire be sure and have the iron well tinned and hot, 
applying the solder quickly and not using too much. If the wire is being 
soldered to a jack spring, a piece of paper should be laid underneath 
where the soldering is done so that small particles of solder will not fall on 
other wires below. In soldering, insert the wire in the notch in the jack 
spring. Don’t heat the wire too much, or insulation will unravel, leaving 
a bare place 1/2 in. or more, which besides being unsightly, is liable to 
cause a short circuit. After soldering, the wires should be laced in shape 
with a button hook, then shellacked in place, using shellac dissolved in 
pure grain alcohol. Don’t use wood alcohol. Have the shellac thin. 

In hunting for trouble in a bunch of wires a device like that shown 
in Fig. 207 will save time. 

A battery should be connected to the end of the wire it is desired to 
find. The other side of the battery is connected to one side of the head 
receiver, while the other side of the receiver is connected to a long needle, 
which can be pushed through the insulation on each wire. When the 
proper wire is located a loud click will be heard in the receiver. This 
is a munh better method than cutting into the wire to locate the trouble. 

Upon examining the Switchboard when it is received from the 
factory it will be found that the wires in the key and line cables are in 
twisted pairs, each twisted pair forming a metallic circuit. Nothing but 
twisted pairs should be used, for if the key or line cable is formed of 
separate strait wires, a great deal of cross talk will result. 

If one cord circuit is carefully tested out and the color and lay out of 
the wires noted, and a sketch made for reference, a great deal of time will 
be saved, as all the cord circuits in the same board are wired alike. 

The usual troubles the Switchboard man has to contend with are 
broken cords, burnt out line drops, and occasionally, but rarely, defective 
jack or key contacts. It may be said that 90 per cent, of the complaints 
against Switchboards may be traced to broken cords, poor operator’s 
batteries, or loose connections between the cable from the Switchboard 
wires to the terminals in the arrester frame. 

The use of soldered connections throughout the Switchboard is un¬ 
doubtedly ideal from a theoretical standpoint, but in actual practice their 
use has not been found satisfactory except in large Switchboards which 
are under the care of experts. 

With all due respect it may be said that the average attendant in the 
average small exchange, does not use a soldering iron with a suffi¬ 
cient degree of proficiency to properly make and unmake soldered con¬ 
nections, therefore the use of machine screw terminals where wires con¬ 
nect to various portions of the equipment, is rapidly coming into use. 

After an experience of several years with this construction, the 
writer would say that same is entirely satisfactory. This is especially true 
in connection with line drop equipment where it is necessary to remove 


MAGNETO SWITCHBOARDS 


149 


drops frequently for repairs to coils. To make and unmake soldered 
connections where the coil is joined to the Switchboard cable, is not only 
a loss of time, but is troublesome, as the wires get shorter and the insula¬ 
tion burns away every time the coil is removed and inserted. With 
machine screw connections, or with the form of construction where the 
drop coil is removed without disturbing any connections, this trouble is 
not present. 

As to screw connections being inferior to soldered connections, it 
may be said that nobody has ever attempted to solder wires fast to a 
telephone, and very little if any trouble occurs from loose connections 
on the top of telephone instruments, and in this case, the connections are 
exposed to rough treatment from all kinds of people. In addition to 
this, where heat coils are used, four contacts are inserted directly in 
the lines, and these rely upon springs for good contact, yet very little 
trouble results. Owing to the ease of making and unmaking screw connec¬ 
tions it is advisable to get equipment where this feature is present as 
much as possible, if the equipment is to be handled by men of little 
experience. 

The selection of a switchboard should be very carefully considered, 
especially as regards size, and the type of equipment peculiarly suited to 
the particular class of service to be given. 



Fig. 208. Fig. 208a. 


The first point to be considered is the probable future growth or 
ultimate size of the exchange. If the contemplated exchange has 40 
subscribers, it is the height of foolishness to buy a 50 line board, for 
with 40 subscribers as the initial number, the community will no doubt 
require one or two hundred ’phones in the near future, after the exchange 
is installed. 

The majority of manufacturers now furnish Switchboard equipment 
so designed that a cabinet can be secured with room for any number of 
lines, the uture growth of the exchange being taken care of by adding 
the additional equipment for the lines from time to time as needed. It 
is not necessary to secure a large amount of equipment in the beginning, 
this to remain idle for some time, but the equipment need only be secured 
as required. 

Perhaps the simplest form of switchboard devised for small 
exchanges is the Fingerboard, the type furnished by The Sumter Tel. 
Mfg. Co., being shown in Fig. 208. Here each line is equipped with a 















150 


TELEPHONOLOGY 


ringer and jack, the ringer being of the same resistance as those used 
in the telephones on the lines. This board is usually used for rural line 
service. Each bell clapper is equipped with a shutter or indicator which 
falls when the bell rings, and thus indicates which line is calling. The 
Western Electric Co.’s arrangement is shown in Fig. 208a and is repre¬ 
sentative of the majority of these devices. 

A plug and cord is connected in multiple with each ringer so that it 
is only necessary to use one plug to connect two lines, this being done 
by putting the plug of the calling line into the jack of the line called. 
When two lines are thus connected together, the bell connected to the 
calling line is left bridged across the circuit and acts as a clearing out 
signal. 

The ringing and talking is done by the operator with an operator’s 
plug, thus eliminating any ringing and listening keys, push buttons or 
other devices, which in a board of this size would tend to make the equip¬ 
ment complicated. 

It will be observed that as each line is connected to a separate bell, 
by Central having a certain signal, the operator need only answer when 
the proper signal is rung. 

The operation of this board is as follows: 

Suppose No. 2 line wants No. 6. A phone on No. 2 line rings, which 
causes bell No. 2 on Switchboard to ring, at the same time the indica¬ 
tor falls, upon seeing which the operator inserts the operator’s plug in 
jack connected to No. 2 line. Upon ascertaining that No. 2 wants No. 6, 
the operator pulls operator’s plug out of No. 2 jack and puts it in No. 
6 jack and rings, and upon getting the party wanted on No. 6 line, the 
operator picks up the No. 2 plug and puts it in jack No. 6. This leaves 
the No. 2 bell connected across the line which acts as a clearing out sig¬ 
nal. If necessary the operator can listen in on the conversation by plug¬ 
ging into the jack of No. 2 line, in which case the No. 2 bell is discon¬ 
nected from the line and the bell in the operator’s set is connected instead. 
These boards are sometimes equipped with regular cord circuits and keys. 

The line circuits of this and all other modern boards, are wired full 
metallic, and can therefore be used on grounded circuits by connecting 
all the wires going to the sleeve or long springs of the jacks together 
and running them to the ground. Each twisted pair in the cable is con¬ 
nected to one of the bells and jacks in the switchboard and usually the 
sleeve wires are covered with solid white, blue or red insulation. 

Fig. 209 shows method of connecting the switchboard to various 
classes of lines, ’phone C being a metallic line, and Phone B a Bridging 
line. Phone B also shows the connection for the last ’phone on a Series 
circuit. Phone A is the middle ’phone on a series line. 

When connecting switchboards particular care should be taken to 
secure a good ground connection for the Switchboard if grounded lines 
are used, or for the lightning arrester if arresters are used with the board. 

The operator’s circuit of this type of switchboard is shown in Fig. 
210. When the use of the board is intermittent, the two coils of dry 
battery may be used for the operator’s transmitter, but in cases where 
the board is constantly in use, bluestone or “gravity” batteries should 
be used. 

The adjustment of the bells in this type of board is practically the 
same as adjusting the bells in an ordinary telephone. Care should be 


MAGNETO SWITCHBOARDS 


151 


taken never to bend the clapper rod as this interferes with the proper 
action of the shutters. 


L /GH TH//VQ- ^RRFSrCR 



A large number of these boards are in use, especially in small 
exchanges, and the reason for the adoption of this type of board was 
primarily due to the fact that a switchboard using ordinary drops does 



not give satisfactory service on Bridging lines where there are a number 
of telephones on each line, owing to the fact that when the telephones 
call each other, the drop in the switchboard falls and the operator not 

































































































































































152 


TELEPHONOLOGY 


being able to hear the number of rings, does not know whether Central 
is wanted or not, and is obliged to answer the call to find this out. There 
has recently been developed several devices to do away with this trouble, 
and these devices can be applied to Switchboards using standard drops. 
Therefore, the ringerboard is now seldom if ever used, it's place having 
been taken by small boards of standard construction using “signal ring¬ 
ing” or “Relay” drops. 

These drops are the same as regular equipment but each time a sig¬ 
nal is projected over the line, the contact A shown in Fig. 211 which 
shows the drop furnished by the Dean Elect. Co., will close a common 
bell circuit and give a signal that can be heard throughout the exchange. 
This ringing of the signal bell follows the number and length of rings 
received over the lines, thus indicating to the operator whether the call 
is for the exchange or whether one subscriber is calling another on the 
same line. The shutter of the drop falls at the same time the signal 
is received, so that when there are a number of these signal relay drops 
in a switchboard the exact line calling will be indicated. To insure 
positive operation, the contacts are platinum pointed. 



Fig. 211. 


Another type of this special drop* is represented by the Unitype Sig¬ 
nal ringing drop made by The Sumter Tel. Mfg. Co., and shown in Fig. 
212 at A. The armature F operates the springs SS so that the contact 
is closed every time the armature is drawn toward the drop coil H. The 
springs SS are long and flexible and very easily operated, and therefore 
faithfully follow the movements of the armature, thus accurately repeat¬ 
ing the long and short rings projected over the line. 

The Shutter E is released at the first impulse, so that the operator 
knows which line is calling, as previously described. 

In all forms of signal ringing drops the regular night bell contacts 
are omitted. 

The bell circuit used in connection with these drops is shown at B 
Fig. 212. It is the same as a regular night bell circuit. Sometimes a 
relay is inserted in the circuit as shown at C, especially if a large bell 
is desired. 

A battery bell having reliable contacts must be used, and so adjusted 
that it will respond quickly when the drop contacts are closed. This can 



MAGNETO SWITCHBOARDS 


153 


be accomplished by giving the bell a rather close adjustment so that the 
armature has no tendency to “tremble”. 

The drop contacts are adjusted so that they close before the arma¬ 
ture is drawn as near the drop core as it will go. This allows the arma¬ 
ture to “rattle” slightly without opening the signal contact and causing 
a false ring. 

These drops can be used in connection with the regular night bell 
circuit of any switchboard, or a separate bell can be used. The arrange¬ 
ment used in Unitype boards is shown in Fig. 213. 


A i 

B 

[_ . -.i 

r^iTl 

A 

_Tf 

i 

1 i | 

w 


C 




Fig. 212. 


Fig. 213. 


The development of the signal ringing drop which can be used in 
regular switchboards, eliminated the type of board using ringers, and 
many types of small drop boards of a few lines capacity for small 
exchanges were developed. Typical of these is the Sumter board shown 
in Fig. 214. 

This board is equipped with an operator’s plug, and in operation is 
practically the same as the ringerboard previously described except 
that after ascertaining the number wanted, the operator connects 
the called and calling party by means of a pair of cords in the usual 
manner, these cords being associated with a bridging clear out drop 
which falls when these parties ring off. To provide means for the 
operator listening in, a listening jack is bridged on the cord circuit. To 
listen, the operator plugs in this jack with the operator’s plug. 

Fig. 215 shows the internal wiring of a switchboard of this descrip¬ 
tion. The circuits of the operator’s set as will be observed, are practical¬ 
ly the circuits of a bridging telephone, therefore when the operator’s plug 
is inserted in any line jack it is simply equivalent to connecting a bridging 
phone to that line. 

The circuit of the connecting cords is very simple, the tip and sleeve 
of one plug being joined to the tip and sleeve of the other. A clear out 
drop of a high impedance and of about 500 ohms resistance is bridged 
across the cord thus enabling the ring-off signal to be secured. 

The drop circuit is the same as that used in all magneto boards. 
Plugging into the line drop cuts off the drop in the usual manner. 













































































154 


TELEPHONOLOGY 


In Fig. 216 is shown the method of connecting one of these boards 
when a lightning arrester of the choke coil or multi-discharge variety is 
used. The upper line in the figure shows connections for metallic lines. 




THIS SHOWS 
CIRCUIT THROUGH 
CABLE 


’ i M 

TERMINAL 
STRIP IN 

SWITCHBOARD 


f WIRES IN 
• SW9D 


CROP 

COiu 


SLEEVE 


GROUND 


Fig. 216 


The. lower line shows a grounded line. The wire X from the sleeve ter¬ 
minal being connected to the common ground wire. 

u.kj*- - 



Fig. 215 

















































































































MAGNETO SWITCHBOARDS 


155 


. ^ is well to mention that the approved method of connecting up 
switchboards is to have the exchange “full metallic” to thef cable box loca¬ 
ted on first pole outside of exchange, and that when grounded circuits 
are used, the wires are made common or grounded at the terminals in 
the cable box. 

. . While one of these small boards may be used with ordinary drops, 
it is much better in all cases where party lines are used, to use the “Sig¬ 
nal Ringing” or “Relay Ringing” drops, which may be used with either 
grounded or metallic lines. 

If the exchange exceeds 20 lines capacity, the wall type cabinet is 
not feasible, as the switchboard rapidly increases in weight. After sev¬ 
eral years of evolution, the accepted type of regular exchange equipment 
is that shown in Fig. 217. The arrangements of the various parts which 
have been described such as cord circuits, keys, drops, etc., is clearly 
shown in Fig. 218 which shows a Dean board which is typical of the 
latest and best practice. 




Fig. 217. 


Fig. 219. 


One particularly good feature of this style cabinet is that boards of 
50, 100, 200 and 300 lines capacity all have the same end dimensions so 
that two or more boards may be set side by side to form one continuous 
board. In this manner when using 100 line sections it is feasible to ope¬ 
rate 300 or even 400 lines, by purchasing 100 line sections as needed, with¬ 
out the use of transfer apparatus. A 100 line section of this description 
is shown in Fig. 219. 

In some rural communities or where the majority of telephones are 
in residences and the traffic not heavy, one operator may handle 200 
lines, then the cabinet shown in Fig. 220 is practicable. 

It should be remembered that the ability of the operator to answer 
calls is limited, and nothing is gained by placing more apparatus in front 
of the operator than can be attended to. 

























156 


TELEPHONOLOGY 


CO^DtMSCRS FOR. CORD CIRCUITS 

for e>tL£CTive sie^AU/Me 

puRPoaes o/nlV, 


KEY POR SWITCrllNO 
TO POWER. RJN<3I/NC> 
SENERATOR.^ 



FOOT RAU_ 

BRASS TUB& 


Fig. 218. 

When the amount of business to be handled cannot be definitely 
decided, it is better to install a cabinet with two operators’ positions like 
that shown in Fig. 221. * 

For toll stations and where tickets are to be made out, etc., a desk 
type cabinet as shown in Fig. 222 is preferable. This can be secured 




















































































































MAGNETO SWITCHBOARDS 157 

for one or two operator’s positions, with pigeon holes on each side of 
the drop space so that toll tickets, etc. can be filed. 



Fig. 220. Fig. 221 


Drawers are also provided where record books can be kept, which 
makes this cabinet more convenient than the regular type for such special 
uses as mentioned above. 



Fig. 222 






















158 


TELEPHONOLOGY 


A great deal of discussion has arisen as to which is the better sys¬ 
tem to adopt, Magneto or Common Battery. Both systems have their 
own advantages. The concensus of opinion of men with years of experi¬ 
ence is that the magneto sytem is more practicable for the average 
exchange not exceeding 500 lines. The principal reason lor this decision 
is that common battery equipment costs more to install, especially the 
storage battery equipment and apparatus for charging same. The com¬ 
mon battery must have experienced men in charge. 

The outside construction must be of the highest quality, and in places 
where the lines run through trees as is necessary in small 'exchanges, 
where cable is not used, the foliage must be carefully trimmed or insulat¬ 
ed wire must be used for the lines. 

The common battery system is impracticable for heavily loaded 
party lines, and a great deal of the business of the average small ex¬ 
change consists of lines of this character. 

If a magneto line is partially short .circuited by the wet limb of a 
tree, or falls down in the road and is partially grounded, it is still able 
to work and give some sort of service; but if a common battery line is 
crossed, the signal in the office is immediately displayed, and remains 
displayed till the cross is removed, which renders service in the mean¬ 
time impossible. 

The manufacture of magneto telephones has reached such a degree 
of perfection that the maintenance of the generator—which is the only 
additional part in magneto telephones as compared with common battery 
instruments—is practically nothing, so that the only saving in mainte¬ 
nance costs between magneto and common battery instruments is the 
batteries used at the subscribers’ stations. 

Now in large exchanges the cost of battery maintenance would be 
very heavy. For instance: in a city like New York, it would be prac¬ 
tically impossible to give telephone service if the batteries in the telephones 
had to be constantly renewed, which would be the case if they were mag¬ 
neto instruments. But in an exchange of less than 500 subscribers, the 
cost of battery renewals with the magneto system would not be such an 
item, when the first cost and maintenance of the common battery is con¬ 
sidered, especially when the batteries on country lines are taken into 
consideration as these would be used with either system as common bat¬ 
tery is impractical for long and heavily loaded lines. 

The exact size of the system that it is most economical to operate as a 
magneto or common battery exchange, depends somewhat on local condi¬ 
tions, but generally the magneto system will be found more satisfactory 
for small exchanges, while for exchanges exceeding 500 lines the common 
battery will be found more economical in cost and maintenance, and su¬ 
perior in point of service. 

One point in connection with this discussion which it is well to keep 
in mind is that the common battery system does not possess any great 
advantage over the magneto in point of operating speed, as that point de¬ 
pends upon the proficiency of the operator lar more than upon the equip¬ 
ment placed in front of her; this, of course, applies to small systems of 
one or two operators only. In the magneto system, the subscriber is 
obliged to turn the crank of the generator when calling Central, whereas, 
in the common battery system, the subscriber simply removes the receiver 
from the hook, and in either case the subscriber is obliged to wait until 


MAGNETO SWITCHBOARDS 


159 


the operator answers. If the operator is properly trained—with either 
system, she will plug into the line jack almost before the subscriber has 
his receiver to his ear. 

The great advantage in point of operation that the common battery 
system has over the magneto, is that the disconnect signal is given auto¬ 
matically by simply placing the receiver on the hook. With the magneto 
system it is necessary to “ring off” by giving the crank a turn, which 
many people forget to do, and this makes it necessary for the operator 
to listen and ask if they are through which is a drag to the service, but 
in small exchanges this is not a fault which seriously interferes with the 
service. 

From time to time various freak magneto telephones have made their 
appearance, in which Central was signalled by removing the receiver, 
and the clearing out signal was given when the receiver was replaced. A 
description of these instruments was given recently in “The American 
Telephone Journal”, from which the following extract is taken: 

“About every so often some enthusiastic Independent conceives the 
idea of revolutionizing telephony so far as the magneto part of it is con¬ 
cerned and devises some new style of “kick coil instrument”. By this 
term is meant one by which the operator on a magneto drop board may 
be signaled without the use of a generator at the subscriber’s station. 
Because it is just about “every so often” the exchange manager persuades 
himself, or some salesman does it for him that this time the proposition 
has really been solved, and into a number of these instruments goes his 
“hard earned”, he to discover only too soon that it is a case of “Stung 
again, by Heck”. Not only does the operator get stung, but so also does 
the manufacturer, who, experiencing an initial rush on the instrument, 
loads up on special tools and material, the mention of which at a latter 
date is amply sufficient to instill a hearty dislike for the one who had the 
unmitigated audacity to suggest such a thing in the first place. 

“The different concoctions of this sort are legion, but as a cold-blood¬ 
ed business proposition do not trust them any further than you can fling 
Taurus by the tail. On account of the multiplicity of these, I will not 
deal with them all but simply take as an example one of the most recent, 
supposing that because it is one of the latest it represents the highest 
stage to which the idea is advanced. 

“The idea featured in this is the common one, that is to use the talk¬ 
ing battery as a means for actuating the switchboard drop. But as the 
talking battery has not sufficient voltage in itself to force enough current 
through the line resistance to cause an actuation of the drop, it was 
found necessary to supply some means for transforming the existing 
conditions as to allow of the desired result being obtained. 

“For this purpose a specially constructed coil is placed in the instru¬ 
ment. This coil is in reality a “step up” transformer, that is it increases 
the voltage and incidentally decreases the amperage. As the output of 
a transformer is in direct relation to the ratio of the number of turns in 
its primary to the number in its secondary, it was deemed necessary to 
make the primary oas low resistance and few turns as possible and the 
secondary just the reverse. So this coil was made with a primary of No. 
18 copper wire of one-half ohm resistance and the secondary of No. 24 
copper wire of one thousand Ohms resistance. 

“The object was to include the primary side of this coil in the bat¬ 
tery circuit for a short period on the upward movement of the receiver 


160 


TELEPHONOLOGY 


hook, depending upon the impulse of high voltage from the secondary to 
cause the switchboard drop to actuate. Fig. 223, shows the diagram of 
the circuit of an instrument so arranged. 

“Greed for force brought in the first obstacle. The one-half ohm of 
the primary is not much of a hinderance to the flow of current and natur¬ 
ally the draw is just about equal to that of a first class short circuit. Of 
course, the contact is only momentary, but it does not take more than a 
dozen calls to raise Hob with the strength of dry cells, which we all agree 
is needed for talking purposes., 

“Next came the discovery that when two kick coil instruments are 
connected through the switchboard and the resistance of the clearing 
out drop is the same or less than of the ringers on the instruments, the 
called subscriber upon answering will actuate the clearing out drop, 
thus advising the operator that the conversation is terminated before it 
has commenced. If she be one of the genus diligent, the operator will 
immediately sever the connection, thus advertising the good service 
afforded by the company and materially assisting the subscriber and en¬ 
larging his profanic vocabulary. 



Fig. 243. 


“From an economic stand-point it is advantageous in a magneto sys¬ 
tem to place series instruments on the single subscriber lines in town, 
but on longer and more heavily loaded lines to use a bridging instrument 
of higher resistance than the series ringers. 

“Imagine now, dear reader, the delight you would manifest when upon 
finishing a conversation with one of your local friends, the proud pos¬ 
sessor of a series instrument, you attempt to gain the attention of the 
operator for a hurry call somewhere else, and although you right man¬ 
fully jiggle the hook, never a peep makes she, for she has been admon¬ 
ished against the evils of working the listening key and to always wait 
for the clearing out signal. However, you do get your former friend 
back again and again because his bell doth jingle right merrily owing to 
the fact that the old truth holds good, and electricity takes the path of 
least resistance, which in this case is through his 80 Ohm bell rather than 
the clearing out drop in the central office. 

“And last, but not least, send your trouble man around to one of these 
instruments and when he unwittingly gets a screw driver or a pair of 
pliers across the right springs in the hook switch, he most assuredly 
will be possessed of the idea that the irascible and implacable brute—that 




































MAGNETO SWITCHBOARDS 


161 


incarnate thunderbolt—that monster of the upper deck—an “old horny 
headed ram”, has struck him fair and hard, at which he will inform you 
in terms in no manner effeminate that you may have your choice of 
either changing your brand of instruments or forthwith put out the 
placard for another bug-shooter. 

“But seldom is anything created for which there is not some time 
some use to which it may be placed to advantage. So when you have re¬ 
moved all of the instruments of the kick coil variety, again secured the 
confidence of your subscribers and explained away the belligerent attitude 
of your trouble man, just quietly remove one or two of these patient pro¬ 
vokers, the kick coil, from the instruments and save them against the day 
when your faithful pole changer shall go on a tantrum, as pole changers 
sometimes do, for connected up in the manner shown in diagram Fig. 224, 
it will carry you over the time of waiting for a new set of springs or a new 
condenser for the pole changer. 

“You will find that from five to ten cells will give you power enough 
to ring all of the instruments on your longest farmer lines as well as 
those locally situated. 



Fig. 224. 


“The wires as marked “To switchboard” should be connected to the 
same posts as the wires from the pole changer. However, it will be 
necessary to also place the key in reach of the operator so that she may 
close it when she desires to ring a subscriber, as owing to the heavy draw 
on the battery it is not desirable to have the vibrator in motion all the 
time. This arrangement might of course be attached in the switchboard 
so as to obviate the necessity of the key, but as this is suggested merely 
in the nature of a “tide over”, we will not enter into details. 

“With a few more dry cells inserted it might also prove a good thing 
to attach on your neighbor’s cat or the salesman who sold you the instru¬ 
ments, on his next visit to you”. 

A very efficient kick coil which will work well with two dry cells 
can be made up as follows (see Fig. 225) : The two cores should be made 
from Norway iron rod three-quarters of an inch in diameter and 3 1-16 
inches long, while the two yokes should be made from Norway iron bar 
with a cross section of three-quarters of an inch by one-half inch. The 
yokes are attached by means of machine screws, three of which are to 
be of iron and the fourth (A) of brass. A thin brass washer (B) sepa¬ 
rates the core from the yoke at the corner where the brass screw A is 
used. This serves to open the magnetic circuit a sufficient amount to allow 
the coh to discharge quickly and thereby produce the maximum effect on 
the line circuit. The spool heads should be made from fibre or hard 
rubber 1 5-8 inches square or in diameter. All of the iron posts should 

li 




























162 


TELEPHONOLOGY 


be carefully annealed before assembling, so as to allow the magnetic 
flux to be set up quickly, as the current flow through the coil is at best 
of very short duration. The secondary winding should be on the spools 
next to the core and should have about 3,700 turns of No. 29 B. and S. 
guage single silk covered wire per spool measuring about 70 ohms, thus 
giving about 140 for the two spools when connected in series. The pri¬ 
mary winding is wound over the secondary and should consist of three 
layers of No. 19 B. and S. guage single cotton covered wire per spool, 
giving about 380 turns for both spools and not over 1.2 ohms total resist¬ 
ance. The figure shows the connection of the windings of the two spools, 
which are both wound exactly alike. The proper connection to the tele¬ 
phone circuit is shown in Fig. 223, the secondary winding or one next to 
cores being marked S in the figure, and the outside or Primary winding 
being marked P. 



As the majority of small switchboards are designed on the unit plan, 
each section being 100 lines capacity, when additional cabinets are added 
from time to time to increase the number of lines, some form of transfer 
equipment becomes necessary, so that the lines ending in front of any 
one operator can be transferred to the position of any other operator to 
be connected to any line ending there as the regular cords are not long 
enough for this purpose. The connection of the said lines is done by 
means of so-called “Transfer” and “Order Wire” circuits. 

For Example. An operator upon receiving a call for a subscriber 
whose line does not terminate on her position, immediately presses an 
order wire push button which connects her talking circuit directly with 
the operator in front of whom the desired line does terminate so as to 
give the necessary directions for the connection. The subscribers are 
then connected by means of a designated transfer circuit. 



There are two kinds of transfer circuits in common use, one of which 
is a two way lamp signal transfer, as shown in Fig. 226 and the other, a 
plug ended transfer is illustrated in Fig. 227. 

















































MAGNETO SWITCHBOARDS 


163 


The two-way transfer extends the subscriber’s line to the distant 
operator’s position so that the latter must then handle the call the same 
as if the line actually terminated on her position, while the plug ended 
transfer extends the calling cord of the first operator to the distant posi¬ 
tion of the other, so that the second operator merely inserts the plug end 
of the transfer into the line designated by the first operator. 

The former arrangement requires the use of two cord circuits to 
complete the connections, but may be used in either direction as its ends 
are exactly alike, while the latter requires only one cord circuit to com¬ 
plete the connection, but more transfers must be provided as they can be 
used in one direction only. 

The operation of the two-way lamp circuit is as follows: The opera¬ 
tor answers the call in the regular manner, and upon finding that a line 
not within her reach is desired, she immediately plugs the calling cord 
of the pair used in answering, into the jack of the transfer circuit which 
terminates on the position in which the jack of the desired subscriber is 
located. This act lights the lamps at both ends of the transfer circuit, 
the one in the remote position serving as a signal for the second operator 
who answers by plugging into the jack associated with this lamp with 
an answering plug of one of her cord circuits. When this plug is insert¬ 
ed both the lamps are extinguished. The first operator then tells the 
second operator the number of the line desired, and the second operator 
completes the connection the same as if the call originated at her position. 



At the termination of the conversation the subscribers < ring off in the 
regular way throwing the clearing-out drops present in the cord circuits 
of both operators’ positions. 



Fig. 228. Fig. 229. 



















164 


, TELEPHONOLOGY 


The lamps at each end of the transfer circuits are lighted when either 
of the operators removes the plug from the jack, thus a check is provided 
on each operator’s action and all chance of tying up the connected sub¬ 
scribers is done away with. 

While this transfer circuit can be operated as just described, the ser¬ 
vice will be greatly improved by the use of order wire circuits which imme¬ 
diately call the distant operator’s attention to the transfer connection 
and give her the necessary directions at the same time. A strip of order 
wire keys is shown in Fig. 228. One key at the calling end of each order 
wire is necessary. When one order wire to each position of every non- 
adjacent operator is necessary the key shown in Fig. 229 is used, which 
consists of a non-locking push button provided with platinum contacts. 
An order wire circuit is shown in Fig. 230. 



In nearly all switchboard cabinets provision is made for installing 
the plugs and lamp jacks necessary for the above described circuit with¬ 
out changing the existing equipment. 

Fig. 231 shows the lamp and jack for one line mounted on a strip. 

The plug ended transfer cord circuits shown in Fig. 227 require a 
special drilling in the plug shelf and special wiring in each position of the 
cabinet at the time the switchboard is made. It is therefore not recom¬ 
mended except in special cases where the original installation of the 
switchboard or the ultimate possibilities require a sufficient number of 
operators’ positions to warrant its use. 

The lamp circuit of this plug ended transfer is operated at the plug 
end by means of a reliable plug seat switch. The outgoing end of the 
circuit requires the same type lamp and jack as is used in the two-way 
transfer circuit. 

A connection is made through a plug ended transfer as follows: 

An operator upon receiving a call for a subscriber whose line termi¬ 
nates in a position beyond her reach completes the connection by ordering 
the distant operator to insert the plug end of a transfer circuit, which 
extends between the two positions, into the desired line. The latter act 
lights signal lamps which remain lighted until the first operator plugs 
into the outgoing jack of this transfer circuit with the calling plug of 
the cord circuit used in answering the subscriber. These signals serve 
as a guard and check on the operator’s movements and effectively prevent 
mistakes in making a connection. The first operator rings the subscri¬ 
ber through the transfer circuit, the same as in making a direct connec- 




























MAGNETO SWITCHBOARDS 


165 


tion, and when the subscribers are through talking and ring off, the clear¬ 
ing out drop in her cord circuit is thrown. When the cord circuit is pulled 
down the lamp signals at both ends of the transfer circuit are lighted 
and remain in this condition until the second operator pulls down the 
transfer plug. This allows of extremely rapid operation, and prevents 
mistakes in connection and insures a complete disconnection of the sub¬ 
scriber’s line. 



Fig. 231. 


The number of transfer circuits necessary in a switchboard depends 
entirely upon the amount of traffic, but under average conditions two or 
three trunks of the two-way type between each position and every non- 
ad jacent position will be found sufficient. When transfer trunks are of 
the plug ended type they can only be used in one direction so there must 
be provided at least two outgoing trunks for each position to every non- 
ad jacent position. In every case, a surplus number of trunks should be 
wired in the cabinets to take care of the ultimate requirements. 

It is usually the practice to use a 10-volt battery to operate the lamp 
signals of these transfer circuits. The following combinations are recom¬ 
mended : 

Fuller, 6" x 8", life 100 ampere hours, 

Edison LaLande, 15 cells type R. R., life 300 ampere hours. 

Gordon No. 1, 15 cells required, life 300 ampere hours. 

Seven Standard Dry Cells. 

The lamps in operation require current of about 2-10 ampere. When 
both lamps are lighted the current consumption may be practically valued 
at i/> ampere. Thus a 100 ampere battery would light the lamps of one 
transfer circuit for a period of 200 hours, and as the lamps are used for 
only a few seconds at a time, the life of a battery is several months or 
more, and depends more upon the attention the cells receive, evaporation, 
etc. 

A multiple trunking system which has met with favor is briefly illus¬ 
trated by the following figures. 

Fig. 232 shows that there are 10 trunking plugs located at each oper¬ 
ator’s position. These plugs are connected in multiple with a jack at 


166 


TELEPHONOLOGY 


each non-adjacent operator’s position. The 0 position has trunking plugs 
10-19; second position, 20-29, third position, 30-39, and so on. It will 
thus be seen that each operator has command of the trunking plugs of 
the adjoining positions should all of her own be in use. 



Each trunking plug is used with a combined ringing and listening 
key which enables the operator at the position where the plug is located 
to listen in on the trunking connection and ring the called subscriber. 

The necessary order wire keys connecting the different operators are 
located immediately adjacent to the trunking jacks. The trunking jacks 
are located in a panel between each two operators’ positions, the switch¬ 
board being arranged in sections of two positions each. 

Fig. 233 shows the circuits of this arrangement, the plugs being loca¬ 
ted in front of the operator at each trunking termination, the multiple 
trunking jacks being located in each non-ad jacent section from which 
the plug is located. Terminals A and B connect to the generator, while 
C and D connect to the operator’s set. 

The operation of the system is as follows: 

Suppose No. 450 desires to call No. 56. Subscriber No. 450, whose 
drop and jack are located in front of operator No. 4, operates the line drop 
which falls. Operator No. 4 thereupon picks up an answering plug on 
her table and inserts it in jack No. 450. Upon ascertaining that sub¬ 
scriber No. 450 desires to connect with subscriber No. 56, she depresses 
the order wire key marked 0 and says, “56”. The 0 operator thereupon 
glances at the row of trunking plugs from 0 to 9, and assigns any one of 
them that is not busy. We will suppose in this instance it is No. 5. The 




























































MAGNETO SWITCHBOARDS 


167 


0 operator thereupon simply anwsers, “No. 5” which tells the 4th opera¬ 
tor which trunk is to be used. Upon assigning trunk No. 5 the 0 opera¬ 
tor picks up trunk plug No. 5 and inserts it in the jack of the No. 56 sub¬ 
scriber^ line. She depresses the ringing key in the usual manner and 
while this operation is taking place, the No. 4 operator is inserting the 
calling plug of the pair of cords she is using to connect No. 450 into trunk 
jack No. 5 which is connected with trunk plug No. 5 of the 0 operator’s 
position. The 4th operator does not ring, as all the ringing should be 
done by the operator at the position where the transfer call terminates. 



Fig. 233. 


When the parties are through talking and “ring-off”, the clear-out 
signal connected to the pair of cords in use at the 4th operator’s position 
will operate, and also the clear-out signal connected to trunk No. 5, which 
signal appears in front of the 0 operator. Both operators thereupon dis¬ 
connect their cords. 

Upon the clearing-out signal being given the connection should be 
taken down in the usual manner. If no disconnect signal is given and 
it is found necessary to take down the plug, the No. 4 operator should 
depress order wire button No. 0 and notify the No. 0 operator by saying 
“clear 5”. 

Should the No. 4 operator receive a call for any 300 or 500 number, 
which are in the position next adjoining, these connections of course may 
be made direct by the No. 4 operator, or by handing the calling plug to 
the operator at the adjoining position and allowing her to insert it into 
the line jack of the subscriber wanted. 

The Order Wire buttons are wired in multiple with the respective 
operator’s telephone sets at each position. 

Where it is necessary to use a Repeating Coil in connection with a 
trunked call, it is only necessary for a cord circuit containing the repeat¬ 
ing coil to be inserted in either end of the trunk. 

When the switchboard exceeds 400 or 500 lines capacity, the arrange¬ 
ments previously described prove unsatisfactory as the distance between 
the first and last part of the board becomes too great to reach with cords 
of ordinary length. When a transfer system is employed considerable 
extra work on'the part of the operator is necessary. 







































168 


TELEPHONOLOGY 


A multiple switchboard is an arrangement whereby any one operator 
can reach all of the lines in the exchange without having to reach an 
undue distance to either side, and without the use of transfer apparatus 
or the assistance of any other operator. 

This is accomplished by a peculiar arrangement of the drops and 
jacks, and by the use of more than one jack for each line, these additional 
jacks being termed ‘‘Multiple Jacks”. 

Fig. 234 is a diagram showing this arrangement. Three sections of 
switchboard are shown for the sake of illustration, it being understood 
that any number of sections may be used. Line No. 100 is shown termi¬ 
nating in a drop and jack in Position 1, the Jack AJ in this position being 
known as the answering jack, and being located adjacent to the drop, or 
in a small panel with the other answering jacks on this position, placed 
below the multiple jacks. 



It is at once evident that the operator upon seeing drop No. 100 fall, 
can plug into the answering jack, and upon ascertaining the number of 
the line desired, for instance No. 300, can plug directly into multiple 
jack 300 with the calling plug of the pair in use, thus connecting the two 
lines with one cord circuit just as if they both terminated in front of her, 
whereas drop No. 300 is located on another section of the switchboard 
far from her reach. 

As a jack for every line is located in each section of the switchboard, 
any operator can connect any two lines on the entire board. 

To prevent more than one connection being made to any line at the 
same time, a ‘‘busy” test was devised so that as soon as one line is con¬ 
nected to another, both lines are made “busy”, this fact being readily 
ascertained by any operator who may attempt to make a connection with 
them, by a click in her receiver, caused by her touching the plug she is 
going to use, to the sleeve or metal throat of the line jack. This test is 
always performed before a connection is made, except when plugging into 
an answering jack, as when answering a call. 

The arrangement of the equipment varies from the forms previouslv 
described. Drops and answering jacks for from 80 to 200 lines being 
placed in front of each operator. Three operators’ positions constitute 
a section, and each section has space for as many multiple jacks as there 
are total lines in the exchange. It is evident that any one of the three 



























MAGNETO SWITCHBOARDS 


169 


operators in each section can easily reach any one of the multiple jacks 
in that section, or can reach the multiple jacks in the end panels of the 
next adjacent sections. An additional group of multiple jacks is placed 
at the left of the first operator and to the right of the last operator so 
that they also can reach all the lines. 

Fig. 235 shows the actual arrangement of a multiple switchboard of 
two sections, arranged for five operators with a total of 1000 lines. The 
extra jack panel for the last operator is not shown in the figure. 

Sometimes the Drops are placed above the multiple jacks, the answer¬ 
ing jacks being located as shown in the figure. This is the case when the 
electrically restored drop is used. 

A little consideration will show that the multiple jacks must always 
be arranged in regular rotation across the face of the board, but that the 
answering jacks and drops need not necessarily be arranged in numeri¬ 



cal order in front of each operator. By means of an intermediate dis¬ 
tributing frame which is described elsewhere, the lines can be arranged 
in front of the operators so that each operator will have an equal num¬ 
ber of busy lines, and therefore an equal amount of work to do. This 
is one of the advantages of the multiple board, and this is not possible 
with other types, as with non-multiple boards, the line jacks and drops 
must be arranged in regular rotation to prevent great confusion. With 
the multiple board the multiple jacks are always used for calling and are 
regularly arranged. The answering jacks are used only when a call is 
answered and in this case the operator is guided to the exact jack by the 
drop signal placed adjacent thereto. 

The capacity of a multiple board is limited by the length and height 
of the sections or jack spaces, that is seldom more than 70 in. long or 36 
in. high, as it would be impossible for the operators to reach a greater 
distance. 

The magneto multiple board came into extended use, but has been 
entirely supplanted by Common Battery equipment, until now lew 
magneto multiple boards remain in service. No attempt to de¬ 
scribe all the varied circuits that have been devised will be made, but 
a few examples will be given to show the development of the type, and 
to enable the operation of modern equipment to be more readily under¬ 
stood. 




























170 


TELEPHONOLOGY ■ 


The series multiple circuit, so called from the fact that the line cir¬ 
cuit runs through the multiple jacks in series as shown in Fig. 236, was 
perhaps the first successful circuit to be used on a large scale. The two 
line circuits A and B shown on the right and left of the figure, each have 
a drop d, one answering jack, and two or more multiple jacks m. m'. 

The insertion of a plug in any one of the jacks opens the drop cir¬ 
cuit and connects the tip and sleeve of the plug to the tip and sleeve of 
the jack in the usual manner. 

The cord circuits are equipped with ringing keys; their operation 
being the same as in non-multiple boards. 



The operation of the listening key is somewhat different, as it is used 
in securing the busy test. Referring to the figure L K shows the listen¬ 
ing key. When thrown this bridges the operator’s set across the cord in 
the usual manner, and also puts a condenser C in series with the tip side 
of the cord to prevent current from the test battery getting into the opera¬ 
tor’s set from the tip of the plug already in a jack, when making a busy 
test, and also to form a path for taking currents so the connection will 
not be broken when the operator “listens in”. 

The operation of the busy test will be understood by reference to 
the lower cord circuit in the figure, which represents an operator in the 
act of testing a busy line. Now assuming a plug to be in any of the jacks 
of line B it will be seen that current will flow from the 6 volt battery, 
though the 500 ohm resistance coil in the sleeve side of the cord circuit, 
and to all of the sleeve thimbles of the line B jacks, thus changing their 
condition and charging them with a — polarity. 

When the operator making the test throws the listening key and 
applies the tip of the answering plug to any .one of the jack thimbles of 
line B or any busy line, current immediately flows from the jack thimble 
to the tip of the plug, and through the operator’s receiver and a 500 ohm 
resistance coil r to the -f- or grounded side of the battery, this causes a 
click in the operator’s receiver which notifies her the line is busy. 



















































































MAGNETO SWITCHBOARDS 


171 


It will also be observed that when a line is in use, the test battery 
can flow over the sleeve side of same through the telephone instrument 
and back to the tip, so that the tip side of the plug in the jack of the wait¬ 
ing subscriber (Line C in the figure) is charged with test battery. Now 
if the condenser was not placed in the operator’s set as shown by the lower 
cord circuit in the figure, no busy test would result, for as soon as the 
listening key was thrown the receiver would be connected to the — side 
of the battery through the answering plug already in the jack. The 
condenser, however, prevents the flow of direct current from the answer¬ 
ing side of the cord, and the busy test is obtained from using the tip of 
the calling plug, as just described, the test not being affected by the an¬ 
swering plug being in a jack. 

It will be observed that no test will result from touching the plug 
on the sleeve of an idle line as no test battery is connected to the sleeve 
of a line jack except when a plug is in a jack of that line. 

Three cells of storage battery are used for the test. The connection 
of the battery through the coils to the sleeve sides of the cord circuits did 
not materially affect the talking circuits or cause “cross talk” owing to the 
high impedance of the 500 ohm coils. 

A 500 ohm bridged clearing out drop, d was used connected across 
the cord as shown. This was operated in the usual manner, when the 
connected subscribers “rang off”. 

Grounded lines could be connected to this type of board, by connect¬ 
ing the sleeve side of the jack to ground through a 500 ohm coil (non 
inductive) to prevent “dead grounding” the sleeve and thereby interfer¬ 
ing with the busy test. 

The drops used in this type of board were of the hand restored type, 
and were mounted over the multiple. Of course mechanically restored 
drops could be used if the drop and answering jack are associated, but 
this type of drop was not developed until this circuit was practically aban¬ 
doned for later and better forms. 

The principal trouble with this circuit was found to arise from the 
series contacts in the jacks. These sometimes failed to close or became 
dirty, and in a large board of many sections this was very serious. It 
would seem that with modern jack equipment this would not occur, as 
jack contacts now seldom give any trouble. In boards of 600 or 800 
capacity, there would only be two pairs of series contacts in the multi¬ 
ple, and recently several exchanges have been equipped with boards using 
the series multiple jack arrangement with modern jacks, and it has 
proven entirely satisfactory. 

Referring to Fig. 236 it will be noted that when a plug is inserted 
in a jack, the tip side of the line is opened, but the sleeve side is not. This 
leaves an open wire (which in a large board may be many feet long) to 
which is attached the drop coil, and this is liable to unbalance the line 
and cause cross talk, especially if the drop coil is not armored and is 
adjacent to another coil. 

As the multiple jacks and wires connecting same constitute the great¬ 
er part of a switchboard of this type, many schemes have been devised to 
lessen the number of wires and jack springs. A board is often termed 
“two wire” or “three wire” multiple from the number of wires use for 
connecting the multiple jacks of each line. 


172 


TELEPHONOLOGY 


This saving in room was very necessary aside from reasons of 
economy, when multiple jacks were larger than they are now. When 
the series multiple board was in use boards of 6000 or 7000 lines were 
considered large, it being impossible to place more than that number of 
jacks in a section. 

With modern equipment, as many as 18000 jacks can be placed in a 
section, the jacks being much more compact. 

The drops used with the series multiple system had to be restored 
by hand. Mechanically restored drops were not in general use, and were 
not adapted to this class of work. The endeavor to automatically restore 
the drop, and to obviate the contact troubles and other troubles in the 
series system, led to the development of the Bridging multiple, or branch 
terminal system. 



Fig. 237 shows the circuit arrangement of this system. The first 
great difference is the absence of series contacts in the jacks, and the 
employment of two sleeves or thimbles. 

The drop used is of the battery restored type, and is shown in Fig. 
238. This is equipped with two coils, the coil c being the coil connected 
to the line and coil d of about 40 ohms, serving to restore the drop. Re¬ 
ferring to the figure, when generator current traverses coil c armature a 
is attracted, rod b is raised and shutter f, which is quite heavy, is released. 
This falls against the projection on shutter g, which is raised to the posi¬ 
tion shown in the dotted lines. This displays the number which is painted 
on the front of shutter f at li. Shutter f only falls outwardly a fraction of 
an inch, and comes to rest against the aluminum shutter g. 

Now supposing a plug to be in any of the line jacks, as shown in Fig. 
237, a circuit can be traced from battery b through winding d, to the ring 
spring r, across the metal ring r' on the plug to the other or grounded side 
of the battery by way of spring g. This current energizes coil d which 
attracts armature f (Fig. 238). This allows shutter g to drop back. Shut¬ 
ter f is prevented from falling when the plug is withdrawn, by the notch 
e in end of rod b. 

Referring to the figure it will be observed that the line winding c 
of the drop is never cut out o p circuit, but always remains bridged on the 
line. It is therefore wound to 500 ohms and armored so as to possess 















































































MAGNETO SWITCHBOARDS 


173 


high impedance, and so as not to cause “cross talk” when the drops are 
mounted close together. 

Only three wires are used in the multiple, the ground g being a com¬ 
mon wire to all the jacks in the switchboard. 

Referring to the cord circuit, it will be observed that the metal ring 
r' on the plug is not connected to anything, but only serves to connect 
springs r and g when the plug is in the jack. It will also be seen that 
the sleeve or thimble marked test does not connect to the plug, but is 
insulated therefrom by the rubber insulation i on the plug. 



Fig. 238. 


After these points have been observed the operation of the circuit 
will be easily understood. Upon a subscriber signaling the central office 
the drop would be energized, and upon seeing the signal the operator 
would plug into the answering jack of the line with the answering plug. 
This would connect the tip and sleeve of the plug with the line springs 
of the jack and also close the battery circuit through the restoring wind¬ 
ing of the drop, causing same to return to normal. 

The operator would then throw listening key L. K. thus bridging her 
receiver and induction coil across the line and placing her in communica¬ 
tion with the subscriber. Upon ascertaining the number desired the 
operator would test to see if the line was busy by touching the plug on 
the test ring or thimble of the jack of the wanted subscriber’s line. This 
test will be described later. Assuming the line to be clear, the operator 
would insert the plug and call the subscriber in the usual manner by 
throwing the ringing key R K. While the drop connected to this called 
line is bridged on the circuit and the ringing current passes through its 
coil, the shutter will not fall because current is flowing through the re¬ 
storing winding and the shutter is locked up, which is the case as long 
as the plug is in the jack. The presence of the drop winding across the 
line does not materially affect the ringing, owing to the high impedance of 
the drop. 

The clear out drop is bridged across the cord circuit. It is construct¬ 
ed same as the line drop. When the subscribers “ring off” it is actua¬ 
ted, and is restored by the operator depressing the listening key, thereby 
closing contacts K, K and putting battery through the restoring coil 
d. It is customary for operators to “listen in” on a magneto cord circuit 
to ascertain if the conversation is finished before removing plugs, as 
subscribers often forget to “ring off”, therefore restoring the clear out 
drop really did not entail any extra work on the part of the operator. 
This method also insured the drop being restored each time before a cord 
circuit was used (as the operator had to throw the listening key to get 
the desired number) which was often not the case with drops that had to 
be restored by hand. 
































174 


TELEPHONOLOGY 


The busy test was accomplished as follows, referring to Fig. 237. 

When the operator depressed the listening key and applied the tip of a 
plug to the test thimble of an idle line, no click would result as the test 
thimble would be connected only to the battery through the restoring 
winding of the line drop, but if the line was “busy” (a plug being con¬ 
nected thereto at some other section of the board) the operator would 
get a click in the ear, caused by current flowing through the receiver and 
induction coil to tip of plug, to the test thimble, to spring r, across ring 
of plug r' to spring g to the ground or other side of battery. This is 
shown in lower portion of Fig. 237. It should be observed in tracing 
circuits in a diagram of this nature that the circuit is completed from 
ground to ground as shown by the dotted lines Fig. 237 even if no line 
is shown, this often being omitted for the sake of simplicity in drawing. 

The battery is also shown in two or three places in the drawing, and 
it should be remembered that in reality, only one battery is used. 

The induction coil used with this system had a primary of 1-3 ohm, 
and a secondary of 150 ohms split in the middle, the ends being connected 
to the receiver as shown. The middle point of the receiver windings or 
the joint of the two coils, was connected to the battery, so that when the 
operator “listened in” on a connection, the circuit would not be unbal¬ 
anced, the ground through the battery being equal on each side of the 
cord circuit when this arrangement is used. This also prevented a 
ground on the line interfering with the busy test. Only one coil of the 
receiver gets current when making the busy test. 

This type of board represents the highest development of the mag¬ 
neto multiple board. The largest board of this type had a capacity of 
9,000 lines. 



> n 





CHAPTER VI. 


SELECTIVE AND LOCK OUT SYSTEMS. 


Selective party line systems may be defined as those where a number 
of instruments are placed on one line and any one signaled from the cen¬ 
tral office without signaling the others. 

A two party or “Duplex” system is shown in Fig. 240. A ringing 
key with two positions is used, or two keys. The phones are connected 
to the line, which must be metallic, as shown. 

When the key is thrown in the J position, the generator is connected 
to the tip line, the sleeve side of the line being grounded at the key to 
prevent the R bell from ringing 

When the key is in the R position, the operation is reversed, the gen¬ 
erator is connected to the sleeve side of the line, the tip side being ground¬ 
ed. This rings the R bell. 



Fig. 240. 



The instruments are usually wired as shown in the-Figure, the tip 
line going to left hand line post, and sleeve to right on the J, and the 
reverse at the R station. A good ground connection must be obtained as 
the bells depend upon this for a circuit. 

It is easy to locate the tip and sleeve sides of the line when connect¬ 
ing the instruments, ask the operator to throw proper ringing key and 
connect the instrument so bell will ring. 

A low wound line drop, (100 ohms) should be used. Calling Cen¬ 
tral and ringing off from these instruments is accomplished the same as 
from an ordinary telephone. 


( 175 ) 







































































176 


TELEPHONOLOGY 


Fig. 240 shows that the ringer is connected from Line 1 to the 
ground through a contact in the generator shunt, this contact being 
opened when the crank is turned and current being thereby prevented 
from going to ground and ringing the other bell on the line. 

Sometimes the instruments are wired as shown at A in the figure, line 
1 being grounded when the crank is turned. 

Switchboards now in use equipped with ordinary ringing keys and 
having cord circuits like that shown in Fig. 180 or 193, may be easily 
adapted for duplex ringing by means of a double throw master key, as 
shown in Fig. 241, and by re-arranging the generator circuit. 

Ordinary telephones can be rung when the cord circuits are equipped 
with duplex keys, by throwing the keys in either position in case the 
line is a metallic one, but when ringing on grounded lines, it is necessary 
to throw the ringing key in the first position, which connects the ground¬ 
ed side of the generator to the sleeve of the calling plug. In this case it 
is supposed that the line wires of grounded lines go to the tip springs of 
the jacks, and that the sleeves are grounded. 



Should a subscriber on a party line desire the other subscriber on 
the same line, the operator should say “Hang up your receiver and I will 
call you.” She then calls both parties by quickly throwing the ringing 
key in both positions. 

The operator should leave a plug in the jack, to denote that the line 
is busy, and to prevent any connection being made thereto until the par¬ 
ties have finished talking and ring off. 

As the modifications of the cord circuit to accommodate duplex ring¬ 
ing are entirely in connection with the ringing equipment, duplex service 
may be given with common battery equipment. In this case it is neces¬ 
sary to insert a two M. F. condenser in series with the ground wire, or 
the line would be grounded through the ringer coils. 

This duplex arrangement will often allow an extensive increase in 
the number of telephones on a system, without having to purchase addi¬ 
tional drops and jacks for the switchboard, and a sudden growth can 
therefore be easily accommodated. 

In case this system is used in connection with common battery work, 
a lock-out relay can be installed in the telephones as described in chapter 
XI, which will give each party on the line secret service without any 
danger of the other party interfering or overhearing the conversation. 






































SELECTIVE AND LOCK OUT SYSTEM 


177 


A Kansas company developed a scheme for duplex service which is 
noticeable as combining alternating and direct current bells, opera¬ 
ted selectively, on a common return system. The plan requires the two 
telephones to be connected in series, one an ordinary 80 ohm series instru¬ 
ment and the other a series instrument equipped with a direct current 
generator and a Schwartz bell, which is intended to be rung by direct 
current, although alternating current will ring it unless hindered in some 
manner. These bells are wound to 30 ohms for lines up to one-half¬ 
mile in length. Over that length 40 ohms is used. If the resistance 
of the winding is too high, the bell will be rung by the alternating cur¬ 
rent used to ring the polarized bell. 

When operated in series with an 80 ohm bell, using current at about 
65 volts, alternated moderately rapidly by a pole changer, it will be found 
impossible to ring the direct current bell owing to the impedance of the 
ringers in series preventing a sufficient amount of current flowing to 
operate it. However, when a direct current of about the same voltage 
is applied to the line, the special bell will respond vigorously, while the 
ordinary polarized ringer will not be affected, except by, maybe, a single 
tap dependent upon the gong to which the tapper may be clinging. 



The additional central office apparatus necessary to operate the sys¬ 
tem on the ordinary switchboard is a two-party selecting key, wired as 
shown in Fig. 242, and a source of direct current, either battery or gen¬ 
erator. It is not practicable to use the same battery as is used on the 
pole-changer, as voltage will vary too widely if other operators are ring¬ 
ing. 

There is no change necessary in order to use the standard cord cir¬ 
cuit with the system, but to avoid false signals from a ring-off a conden¬ 
ser may be inserted in the circuit as shown in the drawing. Only one is 
necessary, inserted in the line side, on a common return system. 

Fig. 242a show’s the two bells as connected on the line. No difference 
has been observed in placing either bell on the end of the line. During 
a conversation either party must talk through the other bell, but this 
seldom causes any trouble. The longest lines on which the scheme has 
been tried, have a working resistance of about 400 ohms, of which 160 
ohms is in the two telephones and heat coils, leaving about 240 ohms as 
the line resistance. This is much higher than the average. The bells 
can be rung on lines of any length, provided the voltage of the ringing 
12 





















178 


TELEPHONOLOGY 


current is high enough to give a current of from .18 to .22 ampere for 
the higher wound bells. 

Four telephones may be rung selectively on one metallic line by the 
“Biased Bell” system. 



Fig. 242a. 

A special generator at the central office is necessary, this to be 
arranged to deliver pulsating currents of either polarity. The construc¬ 
tion of this generator is the same as the ordinary type, except the addi- 



Fig. 243. 


tion of a Commutator, as shown in Fig. 243 at A. This is so placed on 
the armature shaft, that the generator is only in circuit when the pro¬ 
jection A strikes the spring on the side, which is only during a part of 




























































.SELECTIVE AND LOCK OUT SYSTEM 


179 


each revolution. This causes a pulsation of current which is always 
of one polarity (either + or — but never both) depending upon the posi¬ 
tion of piece A in relation to the armature winding. This intermitent 
current always in one direction, is termed “pulsating” current. Often 
in telephone work, this arrangement is referred to as a “direct current” 
generator, and various arrangements of the contact springs may be made, 
so that -f current, — current, or both; or both -f- and — and alternating 
currents, may be obtained from the same generator. Some of the spring 
combinations are shown in Fig. 243. 



Five keys are necessary, arranged as shown in Fig. 244 which also 
shows the instrument wiring. This is the same as in ordinary bridging 
instruments except a special ringer is used, and means for connecting 
the ringer between either side of the line and the ground is provided. 



H. C. Co.’S Attachment. Fig. 244a. Spring Attachment. 


The rine-er, often termed a “Biased bell”, is eouipped with a spring 
which holds the armature to one side as shown in Fig. 244a, this attach- 


















































180 


TELEPHONOLOGY 


ment being readily fitted to any ringer. If the current is in the proper 
direction to affect the coil under the free end of the armature, it will be 
drawn toward this coil, thus causing the ringer to operate. 

As the bells are biased they will only respond to a pulsating current 
in one direction, a reverse current not affecting them. As the direction 
can be changed by so arranging the connections that the current will flow 
through the bells in different directions, 4 bells can be put on one line 
and called selectively. 

The direction of current flow usually used to ring four bells is as fol¬ 
lows : 

Station 1, letter J minus current on sleeve of plug. 

Station 2, letter R minus current on tip of plug. 

Station 3, letter L plus current on sleeve of plug. 

Station 4, letter W plus current on tip of plug. 

The opposite side of the cord is always grounded when ringing, as 
shown in Fig. 244. 

This particular group of letters has been selected from a large num¬ 
ber because they are totally unlike each other in sound, a feature which 
must be kept in mind to prevent a great deal of confusion when the sub¬ 
scribers call for connections. 

When eight parties are put on one line, the letters A. B. F. and I are 
used to denote the additional four parties. These follow in the same 
order and connect same as the J. R. L. and W group. The only excep¬ 
tion is that J is one ring and A two rings with the same key. Both in 
the four party and eight party service when calling central from the tele¬ 
phones, none of the bells on the line will ring. 

Stations are so arranged that station J will have its bell bridged 
from the sleeve side of the" line to ground. Station R, or the second party 
will be bridged from the tip side of the line to ground. The tip line is 
designated as line 1, the sleeve line as line 2, keeps the line in a balanced 
condition. 

Connecting the Telephones. —Fig. 244 shows wiring of the phones. 
The left hand binding post of each instrument connects with the tip line, 
the middle binding post with the ground, and the right binding post with 
line No. 2, or the sleeve line. The four telephones should be connected 
exactly the same, particular care being taken not to reverse the position 
of the lines Nos. 1 and 2. 

Upon the door of each telephone will be noticed two clips connected 
by flexible cords to the bell magnets. The left hand cord is marked A 
and the right hand one B. Directly under these cords are located three 
clips, the left hand one of which is connected to No. 2 line post, the rie-ht 
hand one to No. 1 line post, and the centre clip to the ground post. After 
these points have been observed, the connection should be made as follows, 
or in accordance with the instructions furnished by the manufacturers. 


Station No. 1 or J.A to line No. 2: B to ground. 

Station No. 2 or R.A to line No. 1: B to ground. 

Station No. 3 or L.B to ground: A to line No. 2. 

Station No. 4 or W.B to ground: A to line No. 1. 


When the letters ABF and I are use d for the additional four par¬ 
ties, A is connected the same as J, B the same as R, F the same as L, 






SELECTIVE AND LOCK OUT SYSTEM 


181 


and I the same as W. Particular care should be taken to have the tele¬ 
phones connected in the proper manner, as it is possible to connect them 
and have them ring, and yet not have them connected properly, and this 
is annoying and a hard trouble to locate at times. 

In some makes of instruments, one of the bars in the generator is 
turned around to weaken the magnetism, and is marked to indicate it is 
reversed. If, when all four telephones are connected you cannot ring 
central, turn the reversed magnet around. Do not do this unless abso¬ 
lutely necessary, as when the generator is too strong it may ring the 
bells on the line. It is better to equip the phones with pulsating gener¬ 
ators. 

If two bells ring at once, for instance: if when calling J the W 
bell should ring, the biasing spring of the bell at W should be tightened. 
Be careful in making this adjustment, and do not not bend the springs too 
much. 

Subscribers should be instructed to call for four-party line instru¬ 
ments same as for the two-party phones previously described. 

Calling central and ringing off from four-party instruments is done 
in the same manner as from ordinary telephones. 

The resistance of the bells used in four-party instruments is from 
1600 or 2500 ohms. Generators should be of low voltage. The line drop 
should not be wound to a resistance of more than 100 ohms. It is also 
well to use a low wound clear drop, or to use a repeating coil in the cord 
circuit or one of the special cord circuits described in chapter 5, or when 
“ringing off”, some of the bells on the four party line might tingle. 

Four party selective phones can be used as ordinary bridging phones 
by connecting the A cord on the door to LI clip and B cord to L2 clip, 
and removing the biasing spring from the bell, thus bridging the ringer 
on the line and making the instrument same as an ordinary bridging 
phone. 

While not as elaborate or well suited to the wants of a large ex¬ 
change as some other systems, owing to the necessity of using a ground 
at each station, etc., yet this system, owing to the simplicity of the cen¬ 
tral office equipment is very satisfactory for the small exchange. 

If desired, a master key can be installed in the switchboard, so that 
the four party ringing current can be connected to any cord circuit in 
the switchboard. This is a very good method, and is recommended to 
those who wish to change boards now in use. The circuits are shown 
in Fig. 245. If the best arrangement is desired, each cord circuit should 
be equipped with a separate key, as shown in Fig. 244, as this lessens 
the work of making a connection, as it is only necessary to operate one 
key when ringing. The key marked regular (Fig. 245), simply releases 
any of the other keys that may be down, thus leaving the + current con¬ 
nected for ordinary ringing. 

A pole changer or power generator can be used with this system 
provided same is adapted to give pulsating currents. A resistance lamp 
must be used in the ringing leads of each position, especially if more 
than one operator’s position is used, so as to prevent dead grounding 
the generator if two operators should ring with opposite currents, at 
the same time. 

When used with common battery, it becomes necessary to disconnect 
the bell from the lines except while in the act of ringing, or the line 


182 


TELEPHONOLOGY 


would be grounded through the bell. This cannot be accomplished by 
using a condenser, as the condenser would change the pulsating current 
to such an extent as to make it alternating in character and the bells 
would then ring with any key thrown. 



Fig. 245. 

By using a relay, and wiring the set as shown in Fig. 246 it is pos¬ 
sible to keep the bells disconnected except when ringing. When ring¬ 
ing on the line the contact of the 85A relay closes. This connects the 
bell to line 2 or 1, depending upon the position of the clips which may be 
on A or B and the current passes through the bell to ground 
and back to the central office. The relay is designed to operate 
with ringing current and has a heavy armature of peculiar construction 
so the contact remains closed as long as there is ringing current on the 
line. The condenser does not interfere with the operation of the relay. 

This relay is of 2500 ohms resistance. The condenser also offers 
considerable resistance, and to help deflect the current through the bell, 
one winding of the induction coil, which possesses considerable impe¬ 
dance, is also included in the circuit. This forces most of the current 
through the 2500 ohm bell. 

Another method of adapting this system to common battery, is to 
place in series with the bell, a resistance of about 3,000ohms. This allows 
a very small current to leak through from the central battery all the time. 
This is not enough to operate the line signal or relay, and unless a large 
number of lines so equipped are used, the constant loss of current is not 
large enough to be of importance. 

























































































SELECTIVE AND LOCK OUT SYSTEM 


183 


The Multiple Frequency Central Energy Selective System represents 
an improvement over the older system of Pulsating Spring Adjusted Se¬ 
lective Bell equipment. 

As early as 1899 this system was perfected by Oscar M. Leich and 
has been manufactured since that time by the American Electric Tele¬ 
phone Company. 



In the practical operation of the system as a four-party selective line, 
four instruments are connected to one metallic line (with talking cir¬ 
cuits metallic) ; two of the instruments have their ringing circuits con¬ 
nected between one line wire and the ground, and the other two are con¬ 
nected between the other line wire and the ground. Each pair of in¬ 
struments comprises a high and a low frequency instrument. The 
low frequency instrument is called the “A”, and the high frequency the 
“B” instrument. A selective key having the requisite numb e r of but¬ 
tons is used at the switchboard for ringing, this selective key serving 
the purpose of connecting either high or low frequenccy current between 
either one of the line wires and the ground, that is, sending high or low 
frequency ringing current over the tip or sleeve of the plug and the 
ground. Fig. 247 shows the general arrangement of the four telephones 
on one line, together with the associated ringing key, plug, and genera¬ 
tors. One of the generators delivers 2,400 alternations per minute—> 
this is the low frequency machine. The high frequency machine delivers 
7,200 alternations. The keys, when depressed, operate either of the tel¬ 
ephones marked A, B, C, or D according as either button is actuated. 
Only one of these selective keys, is needed for each operator's position, 
as this key is then used in the capacity of a Master Key. It is preferable 
in those exchanges where a great many selective instruments are used, 
to equip each cord with a four-party ringing key. 

In order to be able to ring the single line or metallic subscribers 
with the regular ringing keys, it is necessary, when a master key is em¬ 
ployed, to depress the button marked AC. These buttons are all lock¬ 
ing, that is, they remain in a depressed condition when actuated, until 
another button is depressed, when the first button is automatically 
released. In Fig. 247 the talking circuit comprising transmitter, indue- 



















184 


TELEPHONOLOGY 


tion coil, battery and receiver, is connected between the two outside line 
binding posts, while the ringing circuit is connected between the middle 
or ground binding post and the right hand binding post. In the figure 
A and C are low frequency instruments, and it is seen that their line 
connections are reversed. The same is true of the two high frequency 
instruments “B” and “D”. It will thus be seen that if ringing current 



Fig. 247. 


of either class is sent over either line wire to the ground, that current is 
sent through the ringing circuits of two instruments, namely, a high and 
low instrument, but on account of the difference in construction of these 
instruments, only one bell will respond, either the high or the low, depend¬ 
ing upon whether high or low frequency curr e nt was impressed on this 
line wire. The same is true of the two instruments having their ringing 
circuits connected to the other line wire on the same circuit. 

Principle of Operation .—In order to cause a selective operation of 
the two bells (the high and the low), condensers and impedance coils are 
employed. 

The arrangement of the ringer circuits in two common battery in¬ 
struments is clearly shown in Fig. 247. The circuits for magneto tele¬ 
phones are shown in Fig. 248, the ringer circuit being the same. 

The low frequency instrument has a ringing circuit comprising a 
ringer of 1,000 ohms, an impedance coil of 2,000 ohms, and a condenser 
of 2 micro-farads capacity, all connected in series. This ringer oper¬ 
ates on a frequency of 20 cycles per second, or less. It is a well-known 
fact that the opposition offered to the flow of an alternating current by 
an impedance coil depends upon the frequency of the current. The 
higher the frequency, the greater is the opposition, that is, the impedance 
varies as the frequency changes—in other words, the impedance is in¬ 
creased by an increase of frequency. Just as it is impossible for any of 
the high frequency talking currents to penetrate or go through a 2,000 
ohm coil, likewise it is impossible for a high frequency ringing current 
to pass a 2,000 ohm coil. A low frequency ringing current, on the con¬ 
trary, readily penetrates the coil on account of the reduced impedance, 




































































SELECTIVE AND LOCK OUT SYSTEM 


185 


and has no difficulty in ringing the 1,000 ohm bell connected in series 
with the coil. In order to obtain an impedance coil in which the impe¬ 
dance may be easily varied artificially, the laminated core is made of E- 
shaped annealed iron punchings, which can be readily inserted and with¬ 
drawn from the coil, if for any reason it is necessary to change the con¬ 
ditions of the coil to adapt the same for unusual line or switchboard cir¬ 
cuit conditions. Adding more iron punchings increases the impedance 
of the coil, and withdrawing the punchings reduces the impedance or 
opposition to the flow of an alternating current. This action of an impe- 



Low frequency 
i , ‘*trc/niemtCikcuit 



High Frequency 
Instrument Circuit 


Fig. 248. 

dance coil to the flow of alternating currents is unlike the action of such a 
ceil to the flow of a direct, continuous current. To the flow of a direct cur¬ 
rent an impedance coil offers a constant resistance irrespective of the volt¬ 
age or amperage of the current, and iron in the coil has no affect on the 
flow of direct current at all, nor does it change the opposition of the coil 
to the flow of such direct, continuous current. The coil is shown in Fig. 
249. 



Fig. 249. 


A 2 M. F. condenser is included in series in the low frequency instru¬ 
ment to prevent a metallic grounding of the line. Thus no battery leak¬ 
age or loss is experienced by the use of this system. The condenser also 
acts in another capacity, being used to supplement the action of the im¬ 
pedance coil. The opposition to the flow of an alternating current 
through a condenser varies with a variation in frequency of the current, 
but this variation is inveresely. Thus the impendance of a condenser, 
that is, its opposition to the flow of an alternating current, decreases with 
an increase in the frequency, and increases with a decrease in the fre¬ 
quency. Thus the condenser may be made to assist in bettering the oper¬ 
ation of the low frequency bell, as it tends to neutralize the effect of the 
impedance coil at the desired low frequency, but has little or no effect in 
















































186 


TELEPHONOLOGY 


opposition to the coil at the high frequency. It is well known that a 
condenser may be chosen of the right size to counteract the inductive 
effect of an impedance coil. 

A high frequency alternating current readily goes through the ordi¬ 
nary condenser, and for this reason a condenser offers little opposition 
to the flow of talking current. The lower the frequency, however, the 
greater becomes this opposition of the condenser, that is, the greater 
becomes the impedance, and thus when we go as low as a direct continu¬ 
ous current, or one having no frequency, such as a battery current, the 
condenser becomes absolutely opaque and does not allow any of this con¬ 
tinuous current to pass through. 

In the high frequency instrument the ringing circuit is arranged with 
a 1,000 ohm ringer in series with a thr e e-tenths micro-farad condenser 
(3-10 M. F.) and a 1,000 ohm impedance coil bridged around the 1,000 
ohm ringer. As explained before, the condenser varies in impedance 
as the frequency of the alternating current varies, and the capacity of 
the condenser is so chosen that it readily permits the high frequency 
alternating current to pass through, but almost absolutely bars the low 
frequency current from passing through, thus the 1,000 ohm ringer or 
bell is readily operated by the high frequency current, while not enough 
low frequency current is permitted to pass through it to operate it. Thus 
the condenser controls the operation of the bell. In order to make the 
action of the ringer more positive, we bridged the 1,000 ohm impedance 
coil around it. This impedance coil will divert low frequency current 
away from the ringer, but is impervious or opaque to the high frequency 
currents, thus forcing them through the ringer coils. The reason the 
variation of impedance in the impedance coil is so much greater than in 
the ringer coils is because the impedance coil has a closed iron circuit. 

By removing iron from the impedance coil of the low frequency in¬ 
strument more current is permitted to go through the ringer coils, while 
a removal of iron from the impedance coil of the high frequency instru¬ 
ment reduces the flow of current in the high frequency ringer coils. 

When the instruments are installed for use, a few precautions must 
be observed, and if these have been complied with, no adjustment of the 
instrument is necessary, no matter what the line conditions. It is neces¬ 
sary to have the gongs on the instrument in such position that the bell 
hammer does not touch either of them when it is resting in its normal 
state on either side. The gongs will thus be struck by the hammer when 
it is operating, due to the elasticity of the arm. This precaution should 
be taken with all telephone ringers whether selective or not. It is fur¬ 
ther necessary to see that the armature of the ringer touches the pole 
pieces when in its normal position on either side. It is also of import¬ 
ance that the ringer armature be securely pivoted in its bearings with¬ 
out any lost motion, so that the armature cannot move up and down bodi¬ 
ly, but is confined to an oscillatory motion. 

In case there is any difficulty experienced in operating the telephones 
on some types of central energy circuits, the first thing that should be 
done is to take a voltmeter reading at the instrument when the ringing 
current is on the line, and if found too low, the switchboard circuit may 
be modified, or the ringing generator capacity increased so that the ring¬ 
ing current is ample. A good ground is always necessary. In case the 
switchboard circuit or ringing generator cannot be changed, a change of 




SELECTIVE AND LOCK OUT SYSTEM 


187 


iron in the impedance coils will serve to change the characteristics of 
the instrument so as to adapt them to entirely different conditions. The 
instruments operate perfectly over a considerable radius of action, and 
the ease of changing their characteristics makes them exceedingly flexi¬ 
ble in their adaptation to all sorts of conditions. 

It is of course apparent that line conditions can not change the fre¬ 
quency of the ringing current, and thus the operation of the instruments 
is independent of line conditions met in practice. 

The instruments are admirably adapted for use on two-party lines, 
in which case there is no necessity for a ground connection. In this case 
it is necessary to use one low and one high frequency bell bridged metal¬ 
lic on the line. 

The advantage of the system lies in the fact that no adjustable 
springs or relays are necessary for their operation, the conditions under 
which the system works being purely electrical in character and not me¬ 
chanical. 

In Fig. 248, the ground binding post (marked G) is shown on one 
side of the line binding posts. This is done for clearness ol illustration. 
In the regular instruments the ground binding post is mounted in the 
centre, between the line binding posts, and the ringing circuit is connected 
between the ground binding post and the right-hand line binding post. 

In order to do away with the older method of spring adjustment for 
four-party Magneto systems, the Zabel 8-party Selective system was in¬ 
vented by Max W. Zabel, and has been marketed extensively by the Amer¬ 
ican Electric Telephone Company. 

In most Magneto Selective systems it is difficult to prevent false sig¬ 
naling of the party line instruments when a party line is connected with 
a single line. When the single line telephone rings off it usually rings 
through the cord circuit and falsely signals some party line instrument. 
This trouble is not apparent in the Zabel 8-party system. 

This system is used very satisfactorily as a 4-party Magneto system 
and also as an 8-party Magneto Selective system. Any number of tele¬ 
phones up to eight can be placed on a line and selectively rung without 
ringing any of the others. 

The principle of the system consists in dividing the eight telephone 
stations into four groups of two each. Each telephone is provided with 
a relay, as shown in Fig. 250, and the two relays of each group are oper¬ 
ated simultaneously. Thus when positive battery current is projected 
on to the sleeve line, relays at stations 3 and 7 operate. When negative 
battery is projected on the sleeve line, relays at stations 4 and 8 operate. 
The same is true with regard to stations 1, 2, 5 and 6, which operate 
respectively when positive or negative battery current is projected over 
the tip line. Normally, all of the signaling bells have their circuits 
open, and they are only closed when the relays operate. Thus, for in¬ 
stance, when the group comprising stations 3 and 7 operate, two signal 
bells are included in the line circuit. The bell at station 3 is included 
between tip and ground, and the bell at station 7 is included in circuit, 
which amounts to the same thing as including it between sleeve and 
ground. If, for instance, positive battery current be projected over 
the sleeve line both relays at stations 3 and 7 operate. At the same time 
this is done, however, if alternating signaling current is projected, say, 
over the sleeve line, the bell at station 7 will operate, but the bell at sta¬ 
tion 3, which is connected to the tip, will not operate. If, however, 


188 


TELEPHONOLOGY 


when the positive battery is connected to sleeve, alternating ringing cur¬ 
rent is connected betwen tip and ground, then the bell at station 3 will 
operate, while the bell at station 7 will not operate. The same is true 
of stations 4 and 8, except that their relays operate with negative battery 
current. Thus you have a selection of four, and in every one of these 
four the relays are connected between sleeve and ground. Now, then, 
to get a selection of eight we duplicate the former stations, but connect 
the relays between tip and ground. An impedance coil is included in 
series with the relay, so that the line will not be affected by noises. The 
impedance coil is wound to over 1,000 ohms. To avoid any tap there 
might be on any bell, the bells at stations 5, G, 7 and 8 are connected in 



the circuit of a secondary coil, wound upon the same core as the above 
mentioned impedance coil, which acts in this case as a primary of a trans¬ 
former. Thus, when the bells of these stations are rung, both the bat¬ 
tery current and the ringing current flows through the relays. The bat¬ 
tery current, of course, will not affect the bell through the transformer, 
and the ringing current will not affect the relay because the relays are 
provided with a copper shell, and thus are not responsive to the influence 
of alternating current, but only responsive to the influence of direct cur¬ 
rent. 

The first four stations are called I stations, and the latter four with 
the transformer coil, are called T stations. 

The system is now manufactured so that no transformer coil, but 





































































































































































































SELECTIVE AND LOCK OUT SYSTEM 189 

merely an impedance, or retardation coil, need be used with the T sta¬ 
tions. 

There is a further distinction between the I and T stations, as will 
be explained later. 

The Figure shows a complete diagram of the eight telephones con¬ 
nected to one metallic line, and shows this line entering a switchboard 
jack and drop and carries the line through the cord circuit, through the 
springs of the eight-party key and from there into the power board and 
voltmeter with which are connected the vibrator, the dry batteries—and 
to the generating equipment which is at present used in the exchange for 
calling subscribers, and which can be either a power generator, pole 
changer or hand generator, and which we have indicated for the sake 
of clearness as power generator shown at G. 

The circuits of all the telephones are shown, the I stations at 1, 2, 
3 and 4 and the T stations at 5, 6, 7 and 8. These telephones can be con¬ 
nected on a metallic line which enters the switchboard drop and jack of 
an ordinary switchboard, which has cord circuits having ringing keys, as 
shown in the illustration. 

It will be seen that to change the switchboard to operate Eight- 
party Selective telephone lines only the Eight-party key need be installed 
Furthermore, the regular ringing equipment which the exchange now 
has in operation will suffice when used in connection with the power 
board, the wiring ol which is shown in this illustration. This is capa- 



Fig. 251. 


ble of accommodating five complete switchboard positions.. Thus the 
Central Station equipment necessary for an exchange consists of one 
power panel and one Eight-party key for each position up to and includ¬ 
ing a total of five positions. 

The 8 Party key is shown in Fig. 251 and is provided with 10 But¬ 
tons, 8 for the 8 party line instruments, one for regular instruments, 























190 


TELEPHONOLOGY 


marked A. C., and a release button R which serves to release any of the 
others, should they be in the depressed position. 

The special relay is shown in Fig. 252. Only these relays are nor¬ 
mally connected to the lines, the bells being normally disconnected. A 
high wound impedance coil being in series with each relay, disturbances 
are kept off the line. 



Fig. 252. 

The Baird Secret Service System represents a type of equipment 
whereby nineteen or less parties can be connected on one metallic line 
and when one party is calling another on the same or a different line, all 
the other phones on the line are “locked out” and cannot hear the conver¬ 
sation. 

This attachment as furnished for use with instruments already 
instiled is shown in Fig. 254, and the circuits of same in Fig. 254a. 

This cabinet is entirely separate from the telephone proper. The 
visual signal, as seen through the window in the cabinet, at once indi¬ 
cates to the subscriber whether the line is “clear” or “busy”, without 
removing the receiver from the hook. 



The Emergency Call button makes provision whereby any “locked- 
out” subscriber can, in case of urgent need, signal Central Office. 

The Method of connecting the Attachment to standard bridging tel¬ 
ephones now in use is shown in Fig. 255, which shows the changes in 
wiring necessary in standard bridging telephones, when used in connec¬ 
tion with the Secret Service Attachment. Simply open up one side of 



















































SELECTIVE AND LOCK OUT SYSTEM 


191 


ringer and carry it out to binding post D, then add one new wire from 
the common point of the primary and secondary on the induction coil to 
post C. Connect the wires of the attachment to the telephone, and it is 
ready for Secret Service. (Binding posts C and D may be dispensed 
with if desired by running wires directly from Attachment to Telephone.) 

The Central Office Calling Device, as shown in Fig. 256 contains the 
mechanism necessary in selecting and automatically ringing the party 
desired, and locking out all others on a party line equipped with the 
Secret Service apparatus. It is generally placed on the key shelf or 
mounted in a convenient place, easily accessible to the operator, and is 
connected into the cord circuits of any magneto switchboard, as shown 
in Fig. 257. 



Fig. 254. Fig. 256. 


It is necessary to disturb the existing wiring only to the extent of 
opening up the answering and calling cords, and connecting the Calling 
Device in series in the manner shown. The cord circuits that are so 
equipped may be used for regular service when not in use on Secret 
Service lines. 

Description of the Electrical Operation of the Baird Secret-Service 
System. —The Subscriber rings down the line drop with an alternating 
current from the subscriber’s station “full metalic” in the regular man¬ 
ner. The operator answers. After ascertaining his number she oper¬ 
ates her Calling Device which automatically sends impulses first from the 
50 volt battery and then from the 12 volt battery alternately out over the 
line “full metallic”. This operates every one of the step-up mechanisms 
along the line. At the time this stepping-up mechanism is going on and 
say, for instance, party No. 6 is the party we desire to call, locking him 
in and locking all the rest, this locking-in subscriber No. 6 is accom¬ 
plished as follows: The Calling Device is arranged so that the first 
impulse is used for automatically clearing the line at the beginning of 
a call, should the operator have failed to do so when she received her 
clearing out signal the last time that the party line was in use. The 
first impulse, therefore, that affects the subscribers’ mechanisms is really 


































































192 


TELEPHONOLOGY 


the second one sent out from the Calling Device, therefore if subscriber 
No. 6 is the party to be called the operator will have had her plug in her 
Calling Device at No. 6. At the 7th 50 volt impulse from the Calling 
Device the little wiper on the ratchet wheel at station No. 6 is in contact 
with the locking-in coil spring. At that very instant also, the lever on 
the Calling Device handle is passing the plug on the Calling Device. The 
passing of this little lever over the plug in the Calling Device dial will 
cause an alternating current to flow out over the sleeve side of the line 




through the frame of the mechanism at station No. 6, through the wiper 
on the ratchet wheel, through the locking-in coil spring, through the 
locking-in coil to the ground, thus causing the armature of the locking- 
in coil to operate the group of contact springs which lock subscriber No. 
6 in on the line for conversation. The wiper, on coming in contact with 
the locking-in coil spring, stays there for only one impulse, passing off 
on the eighth impulse, therefore taking the ground off the line for talk¬ 
ing. This action is the same for any number of subscribers along the 
line, according to the plugs that the operator inserts in her Calling Device 
dial at Central. 

The ringing is done over the sleeve side of the line to ground auto¬ 
matically for a short period by the Calling Device just before it comes 
to its normal position, and after 20 impulses have been sent out over the 
line. If the subscriber falls to answer with this short automatic ririg, 
the operator rings him as often as she desires manually, by simply press- 












































































































SELECTIVE AND LOCK OUT SYSTEM 193 

ing the ringing button situated beneath the key on her calling device, 
which is in service with the pair of cords used to make the connection. 
This manual ringing is also done over the sleeve side of the line through 
the lower contact of the switchhook, through the ringer to ground, 
through the contact which has already been established, through the set 
of springs actuated by the locking-in coil. The above covers the descrip¬ 
tion as far as the desired subscriber is concerned. 

After the conversation, the party who has been using the line turns 
his hand generator and clears-out with an alternating current in the usual 
manner, by actuating the clearing-out drop of about 500 ohms, perma¬ 
nently bridged across the cords. 

After receiving the clearing-out signal the operator actuates her 
key in the Calling Device, thus throwing a 50 volt battery of opposite 
polarity out onto the line to clear it, or, in other words, restoring same 
to its normal position. 


CORD - LINE & SUBSCRIBER’S 



The operation of the Emergency Call Button is very simple. If a 
subscriber having an urgent call desires to signal Central, he presses his 
Emergency Call Button and turns his hand generator. This throws an 
alternating current over the line “full metallic”, thus throwing the clear¬ 
ing-out drop at Central Office. 

Subscriber Calling Central. —To call Central, the subscriber TURNS 
HIS HAND GENERATOR at the subscriber’s station instrument, LEAV¬ 
ING HIS RECEIVER ON THE SWITCHHOOK. This causes an alter¬ 
nating current to flow over the line “full metallic” to Central Office, actu¬ 
ating the line drop corresponding to the party line from which the call 
is made, notifying the operator that some one on that line desires service. 

Operator Answering the Call. —The operator inserts her answering 
plug in the jack of the line signalling. She then moves her listening key 
to listening position and requires the calling party’s number. This, we 
will say, is No. 5. Operator then ascertains the number desired, say 
for instance, No. 15 on the same party line. The operator thereupon 
restores her listening key to its normal position. She next inserts a 
peg in No. 5 and another in No. 15 of the Calling Device dial, after which 
she turns the lever around the dial until it comes to a full stop and locks. 

13 



































































194 


TELEPHONOLOGY 


She then operates the key lever, (which is directly under the dial) cor¬ 
responding with the pair of cords used in making the connection. By an 
upward movement of this lever the Calling Device is released and returns 
around the dial to its normal position. By this action the Calling Device 
automatically sends out on the line a series of Direct Current impulses, 
causing the Lock-Out mechanism, (which forms a part of every subscri¬ 
ber’s instrument) to operate. This operation locks out all of the sub¬ 
scribers along that party line, whether their Receivers are on or off the 
Hook, except parties No. 5 and No. 15. 

The Calling Device, upon its return from the operated position to 
normal, not only operates the Lock-Out mechanism at the several sub¬ 
scribers’ stations, but also Automatically Rings the Party Wanted. (The 
one in this case being No. 15.) Should the party fail to answer his tele¬ 
phone on this first ring, the operator can ring him as often as she desires 
manually, by simply pressing the ringing key button, located directly 
below the key lever previously operated. When party No. 15 answers, 
he is in direct communication with subscriber No. 5. 

Operator Clearing Out or Restoring the Line to Normal. —After 
parties No. 5 and No. 15 have finished their conversation they hang up 
their receivers, and turn their hand generators in the usual manner. 
This actuates the clearing-out drop at Central, and notifies the opera¬ 
tor that the parties on that line have finished their conversation. She 
thereupon operates the key lever under the dial of her Calling Device 
(corresponding to the pair of cords with which the connection was made), 
by an upward movement in the same manner as when releasing the Call¬ 
ing Device lever in sending out the call. This action sends a direct cur¬ 
rent (of opposite Polarity to that used in stepping up this Lock-Out 
mechanism in the first instance) out on the line, restoring to normal the 
Lock-Out mechanism of every subscriber’s instrument on that party line. 
She next removes the answering plug from the line jack and the line is 
again at the disposal of any party on it. 

The operation of connecting one line with another is slightly dif¬ 
ferent from the above, but the various operations of locking the subscri¬ 
ber in, etc. are the same. 

When properly installed these instruments need little attention, and 
the re-adjustment of the lock-out mechanism should never be attempted 
except as a last resort, and then only by some one who is throughly com¬ 
petent to make such adjustments. 

The 50 and 12 volt batteries must be kept at the proper voltage. 

The line troubles must be promptly cleared as they of course affect 
this system to a greater extent than on ordinary line. If selector works 
backwards line is reversed. 

This system is typical of step-by-step devices. Hundreds of patents 
have been taken out on devices of this nature, but with the exception of 
this and one or two similar systems, they have never come into extended 
use. 


The Homer Roberts selective and lock-out system represents a type 
of equipment wherein the different stations are only connected to the 
line when wanted. As many as forty instruments can be put on one 
line. The following describes in detail the manner of operation and the 
equipment. 


SELECTIVE AND LOCK OUT SYSTEM 


195 


Paragraphs 1 to 21, inclusive, refer particularly to the line and sub¬ 
stations, while paragraphs 22 to 35, inclusive, take up in detail the cir¬ 
cuits and mechanism at central in their relation to those of the line and 
substation. 

1 The Selection of a given Station. Fig. 258 represents diagram- 
matically a line of 4 stations, the instruments all being shown in their 
normal condition. The tip, or left side of the line, is shown as an unbro¬ 
ken conductor, to which is connected at each station the biased ringer B, 
and, in series with the latter, the coil A, which represents the selecting 
relay. The sleeve or right side of the line is broken at each station, the 
outer end of each section terminating in a switch lever 2, which is shown 
resting on a contact 1. Obviously, if a proper ringing current be sent 
over the line from central, the bell at station 1 only will operate, since 
the circuits of the other ringers are not completed. If now, the switch 
levers at stations 1 and 2 are moved out of engagement with contacts 1 
and into engagement with contacts 3, we have the condition shown in 
Fig. 259. Station 3 is now in circuit and its bell may be rung, the instru¬ 
ments 1 and 2 being disconnected from the right line at contacts 1, while 
station 4 is still cut off at the contact 3 of station 3. 


ceft I JL HL UL 



Left i u m m 



Fig. 259. 


2 The Selecting Relay. Fig. 260 shows the selecting relay, and 
Fig. 261 shows diagrammatically the elements of same. The instrument 
resembles in construction the ordinary polarized ringer. When current 
is sent through the coil A in the proper direction the end of the armature 
carrying knob K is depressed, and pushes down spring 1 against the ten¬ 
sion of springs 2 and 3, the latch L engaging with spring 2, while the 
stud P prevents springs 2 and 3 from prematurely coming together. 
When the current through coil A ceases, springs 1 and 3 rise (2 being 
held by the latch), and 3 closes contact with spring 2, as shown in Fig. 
262. 






















































196 


TELEPHONOLOGY 


3 By referring to Figs. 263 and 264, it will be seen that spring 2 
performs the same functions as switch lever 2 in Figs. 258 and 259. Fig. 
263 shows a line of 4 instruments in normal condition. To ring the bell 
at station 1 it is only necessary to send to line pulsating current of the 
proper direction. Although this ringing current passes through the 
coil A, it does not affect the selecting relay, which is adapted to be opera¬ 
ted by current of the reverse direction only. The bells at stations 2, 3 
and 4 do not operate as the circuit is open at each spring 3. Suppose, 
however, it is desired to call station 3. If a reverse impulse be sent out 
over the line, current flows through the coil A and ringer B at station 1. 



Fig. 260. Wall Set. Fig. 260. 


This current is of the right direction to operate the relay and not to ring 
the bell. Under the influence of the current through coil A, the armature 
of the selecting relay is depressed, bringing the spring 2 under the latch 
L. At the end of the impulse spring 1 returns to its normal position, 
and spring 3 rises into contact with spring 2, which is prevented from re¬ 
turning by the latch L. Station 1 is now cut out of circuit at spring 1, and 
station 2 placed in circuit by the closing o c the contact between springs 2 
and 3. Current of the right direction thus to latch up the selecting relays 
will be hereafter designated passing current. Another passing impulse 
sent to line will in the same manner latch up the relay at station 2. Fig. 
264 shows the condition existing after two impulses have been sent to line. 
It will be seen that stations 1 and 2 are cut off from the circuit which is 
now completed to station 3 through the springs 2 and 3 at station 1 and 
station 2. Ringing current sent out over the line will now ring the bell at 
station 3. 























SELECTIVE AND LOCK OUT SYSTEM 


197 


4 Restoring the Line. It is obvious that some means must be pro¬ 
vided for restoring the selecting relays to normal after a conversation 
is finished. By referring back to Fig. 262 it will be seen that the upper 
end of the latch spring L is bent over in such a manner that when the 
armature is attracted by current flowing through the coil D, the knob K 
on rising engages with the bent cam surface and forces back the latch 
L, permitting spring 2 to return to its normal position as shown in Fig. 
261. 

5 The coils D are placed in series with the unbroken side of the 
line, one at each station, a temporary ground at the end of the line being 
employed to obtain a circuit through all the coils D simultaneously. This 
temporary ground is obtained by the use of a “grounding” relay at the 
end of the line. The relation of this instrument to the circuit is shown 
in Figs. 263 and 264. To restore the line the operator sends out enough 
additional passing impulses to extend the circuit to the end of the line, 




and thus brings the grounder G into circuit. This instrument is similar 
to the selecting relays, but is normally in latched position as shown in 
Figs. 263 and 264. The winding of the grounder G is connected in such 
a manner that the next passing impulse throws off its latch, permitting 
spring 1 to contact with the ground spring 2. The operator now sends 
a grounded impulse to the left line, current flowing over the left limb 
through the coils D and the left hand spool of the grounder G to ground. 
The selecting relays are therefore simultaneously restored to normal. 
The grounder G is also energized and restored to its normal position. 

6 Differential Winding. Although the coils D are of low ohmic 
resistance, it is evident that if a party were talking through a number of 
stations the impedance thus present in the le t line would affect the talk¬ 
ing efficiency to some extent. To prevent this there is inserted in the 
right line at each instrument a coil similar to D and wound on the same 
spool, connected in such manner as to neutralize the self induction of coil 
D, as regards current flowing over the metallic circuit. These coils are 
shown in Fig. 265. These neutralizing windings also prevent any tend¬ 
ency to unlatch intermediate relays when ringing a bell beyond. 

7 The Ringer. Thus far the ringer B has been considered only as 
an ordinary biased bell. This instrument, however, also controls the 
talking circuit of the subscriber. To do this it is provided with a set of 
contact springs operated in a manner similar to those of the selecting 









































198 


TELEPHONOLOGY 


relay. When the bell is rung the first stroke of the armature unlatches 
the group of springs and places the subscriber in talking circuit. When 
the operator passes on beyond that station the same impulse that latches 
up the selecting relay also latches up the group of springs on the ringer 
and thus locks out the station. Fig. 266 shows the general appearance 
of the ringer. 



Fig. 263. 


I l t j t 2L HL HL 



8 Referring to Fig. 267, which shows the device in normal (latched) 
position, it will be seen that in many respects it is similar to the selecting 
relay. To enable the instrument to operate both as a ringer and relay 
without interference between the two functions, the tapper rod is pivoted 
in the armature and provided with a projection on one side, with which 
the armature engages when the latter moves in ringing direction. The 
tapper remains at rest when the armature moves in the other (latching) 


i e nr 



direction. By referring to Fig. 267, it will be seen that springs 2 and 3 
are normally closed and all other contacts are normally open. The un¬ 
latched or talking position is shown in Fig. 268, the contact between 




























































































































































































































































SELECTIVE AND LOCK OXJT SYSTEM 


199 


spring 2 and 3 being open, and the springs 4, 2 and 1 being connected by 
the upward pressure of the contact pin P. It may be noted that spring 
5, which is hooked over spring 4, is never in contact with the latter except 
momentarily while the armature is depressed in passing (latching) direc¬ 
tion. 



Fig. 266. Fig. 267. Fig. 268. 


9 The relation of the ringer contacts to the subscriber’s talking 
circuit is shown in Fig. 265, which represents a line of 3 stations with 
station 1 in passed condition, station 2 in talking circuit, and station 3 
normal. It will be noted that at stations 1 and 3 the receiver is short 
circuited by springs 2 and 3, and the listening circuit is also open at 
spring 2. The local battery circuit is also open whether the hook is up 
or down, since springs 4 and 1 are not in contact. At station 2, which 
is in talking circuit, the receiver circuit may be traced from the left line, 
the upper hook-switch contacts, springs 4 and 2, receiver, secondary, con¬ 
denser, to the right line, and the transmitter circuit may be traced 
through the left line, primary, battery, transmitter, springs 1, 2 and 4, 
and the hook-switch upper contact. It will be seen from a careful inspec¬ 
tion of Fig. 265 that owing to the condensers C the continuity of the line 
for talking purposes is not affected by the position of the selecting relay 
contacts. 



Fig. 269. 


Master Key. 




















































































200 


TELEPHONOLOGY 


10. Signalling In. A central battery is used to operate the 
line signals, which are ordinary drops. On reference to Fig. 269, it will 
be seen that one pole of the drop battery is grounded, and the other pole 
connected to the winding of the drop, which is connected with the tip or 
left side of the line through spring D. To call central, a subscriber sim¬ 
ply takes his receiver from the hook. The three contact springs of the 
hook-switch are so adjusted that when the hook rises the middle spring 
makes contact with the top spring before it breaks contact with the bot¬ 
tom spring; all three springs being thus connected during the central por¬ 
tion of the movement. The flash circuit thus formed may be traced from 
ground through the three springs of the hook-switch, the left side of the 
line, through the line jack contacts to the drop and through the drop and 
battery to ground. The drop is thus operated, the shutter falls, and the 
operator plugs in. 



Desk Set. Fig. 270. 


11 Answering Calls. Since, however, all parties on the line are 
normally locked out of talking circuit, some means must be provided 
whereby the operator may place the signalling party in talking connec¬ 
tion and leave all the other instruments on the line in their normally 
locked out position. In fact, the operator must be able automatically to 
pick out the station that signalled in, and operate the ringer to unlatch 
the springs controlling the talking circuit. 

12 Fig. 270 shows (stripped of all detail) the means employed to 
pick out in this way the station signalling in. When the operator presses 
key R, passing impulses flow out over the metallic circuit and sucessive- 
ly operate the intervening relays, extending the circuit to the station 
shown. When the current starts to flow through that station the arma¬ 
ture of the ringer is depressed and closes the contact between springs 5 
and 4. This establishes a circuit from ground through springs 5 and 
4 of the ringer, the hook-switch upper contact (the receiver being re¬ 
moved from the hook) over the left side of the line, through battery M 
and relay A to ground. This operates the quick-acting relay A at central. 









































SELECTIVE AND LOCK OUT SYSTEM 


201 


The operation of the latter opens the circuit of the right line and so pre¬ 
vents the operation of the selecting relay at that station. Ringing cur¬ 
rent is then sent to line; this unlatches the ringer springs and places the 
subscriber in talking circuit. As a matter of fact a single impulse is 
thrown on automatically by the operation of the relay A, although for the 
sake of clearness this is not shown in Fig. 270. 

13 If a party signals when the line is busy, he gets no response from 
central. Assuming that the line is busy, he will simply leave his receiver 
off the hook. When the party who is using the line hangs up his receiver 
the supervisory signal is displayed (as explained later) and the operator 
then locks out his instrument and passes his station with one passing 
impulse. On again throwing over the key R the waiting subscriber is 
automatically selected in the same manner as was the first party. If 
there are no subscribers waiting for service the relay A will not operate 
until the grounder at the end of the line is unlatched, the selecting relays 
being then restored to normal automatically (as explained later). After 
a conversation is finished the whole line should be tested with the key R 
to avoid missing any waiting subscribers nearer central than the one pre¬ 
viously using the line. 

14 Supervision. —The supervisory signal for each end of the cord 
circuit consists of a lamp controlled by a relay or a mechanical signal of 
the central energy type. The latter is shown in Fig. 269. If a subscri¬ 
ber is in talking circuit and he replaces his receiver on the hook he estab¬ 
lishes a circuit frpm ground at his instrument through the lower hook- 
switch contacts, the ringer springs 4 and 1, the primary circuit, over the 
left limb of the line to the tip O' jack and plug and through the mechani¬ 
cal signal and battery to ground. This operates the cord signal and noti¬ 
fies the operator to disconnect. 

15 Emergency Signal. —If any party wishes an emergency connec¬ 
tion when the line is in use he moves his receiver hook up and down for, 
say six or eight times. Each movement of the switch hook momentarily 
brings the three springs together giving a flash ground circuit over the 
left line through the cord signal, which causes the latter to wink. The 
series of winks notifies the operator that an emergency signal is being 
sent in. The operator then throws off the party or parties using the line 
and picks up the emergency signalling station. 

16 The Grounder. —In Figs. 263 and 264 the grounder is shown as' 
being an instrument similar to the selecting relay, but with one winding 
only. As will be seen later, it is desirable to be able to restore the select¬ 
ing relays to normal position without being required to run past the end 
of the line and unlatch the grounder. To do this it is obviously necessary 
to establish a ground at any time at the end of the left limb of the line, 
and it is also necessary to be able to release this ground after the restor¬ 
ing operation. 

17 Referring to Fig. 265, which shows the grounder G in its normal 
position, it will be noted that the end of the coil K is grounded through 
a condenser. If a grounded battery of the right polarity be applied to 
the left line the condenser will receive a charge which will pass through 
the coils a and K. This will cause the armature to be depressed, closing 
the contact between springs 1 and 2. When this occurs, a direct holding 
circuit may be traced from ground through springs 1 and 2, and the coil 
a to the left line, allowing the current to flow from central over the left 
line through coil a which holds the contacts 1 and 2 closed as long as the 


202 


TELEPHONOLOGY 


current is on. The coils D of the selecting relays being included in the left 
line are at the same time energized and restore to normal whatever selec¬ 
ting relays have been operated. When the current is removed the coil a 
is de-energized and the spring 1 raises the armature, the contact between 
springs 1 and 2 is broken and the ground released. 

18 When restoring the line in the usual manner as previously de¬ 
scribed in Par. 5, the last passing impulse kicks off the latch L and the 
spring 2 rises into contact with spring 1 and spring 3 rises out of contact 
with spring 4. The reason for opening the circuit between springs 4 
and 3 will be explained later on in the more detailed description of the 
central equipment. 

19 Connecting Two on the Same Line. —If a subscriber wishes to 
talk with a party on the same line, he must call central in the usual man¬ 
ner by taking off his receiver. On being automatically picked out and 
placed in talking circuit by the operator he will give her his number and 
the number required. Suppose he is No. 5 and wishes to talk with No. 3. 
To call No. 3 it is necessary to have the selecting relays in normal posi¬ 
tion. The operator therefore restores them to normal in the manner 
described in Par. 17. She then selects and rings No. 3 in the usual man¬ 
ner, this act completing the connection. The talking circuit of No. 5 is 
not destroyed by the unlatching of the selecting relays, as, although the 
contacts between springs 2 and 3 at stations 3 and 4 are now open, the 
voice currents between the two subscribers pass freely through the con¬ 
densers bridging the gaps. These condensers (which are shown at C 
in Fig. 265), being of small capacity, do not interfere with the proper 
operation of the bells and relays. 

20 Suppose, however, No. 5 calls for No. 7. To ring No. 7 the oper¬ 
ator sends to line two passing impulses and then throws on the ringing 
current, which places No. 7 in talking circuit. The first passing impulse 
however, which passed station 5, besides latching up the selecting relay, 
at the same time latched up the ringer at station 5, which is therefore 
thrown out of talking circuit, and it is necessary to give back to No. 5 
his talking connection. To do this the operator restores the selecting 
relays in the manner previously described, and then selects and rings No. 
5, the two parties then being connected. 

21 In either case after the two parties are through talking, the 
operator must first send to line a sufficient number of metallic passing 
impulses to latch past the further instrument, both subscribers then being 
locked out. She then clears the line in the usual manner. 

The Central Office Equipment and its Operation. —Four Key move¬ 
ments are employed to perform the various operations of the system, viz: 

22 (1) PASS. —This key movement simply passes one station. If 
that station is in talking circuit, it also latches up the ringer group and 
locks out the subscriber. 

23 (2) RING OR SELECT. —This key movement simply rings 
on the line; when used in combination with the dial selector, it selects and 
rings the particular station desired. 

24 (3) RESTORE. —This key movement restores to normal what¬ 
ever selecting relays have been latched past regardless of whether the 
line has been partially or wholly built up. 


SELECTIVE AND LOCK OUT SYSTEM 


203 

25 (4) RUN .-—This picks out and places in talking circuit any 
subscriber who has signalled. If there are no calling subscribers waiting, 
the line is automatically restored to normal condition. 

26 All these operations may be performed on either end of any cord 
pair, the same selective apparatus being used in each case. To permit 
of this without undue complication of the cord circuit, a special key is 
used in each cord circuit which enables any pair of cords to be trunked 
over to the master key set, of which latter there is one provided in each 
operator s position. As the operator’s listening circuit is bridged across 
the master key set, she is enabled to listen in when she throws over the 
cord key, which locks like a regular listening key. The master key set 
is also provided with supervisory signals which take the place of the regu¬ 
lar cord signals when the cord key is thrown over. 

27 Fig. 271 shows the special selective equipment for one position. 



Fig. 272 shows the selector mechanism. To avoid confusion only one 
end of the Master Key is shown, one-half of the cord trunking key being 
omitted from the diagram for the same reason, Fig. 269 showing the 
cord circuit proper. D indicates the battery used to operate the super¬ 
visory signals and drops. The battery B supplies the current used to 
operate the bells and relays out on the line. At P is indicated the vibrat¬ 
ing reed of a pole changer, which transforms the direct current of the 
battery B into pulsating current of two polarities. The local battery 
which vibrates the pole changer is shown at L. 

28 Picking up Signals .—To call central the subscriber takes off his 
receiver, this act throwing the drop as previously explained. The opera¬ 
tor then plugs in and throws over the cord key which places the master 
key in operative relation with the line. Pressing the running key then 
closes a circuit from the 4- pole of the pole changer through 200m; re¬ 
sistance, springs 7 and 6 of relay A to sleeve side of running key and over 


































































































204 


TELEPHONOLOGY 


sleeve to line and the external circuit, returning over the tip to the out¬ 
side contact on tip side of running key, springs 3 and 4 of A relay, to the 
negative pole of the battery B. Passing impulses therefore flow out over 
the line and successively operate the selecting relays, extending the cir¬ 
cuit to the party who has removed his receiver from the hook. As soon 
as the current starts to flow through that instrument the armature of 
ringer and relay commence to move in latching direction. The instant 
the ringer armature begins to move, however, it closes the contact be¬ 
tween springs 4 and 5. This closes a circuit from ground through springs 
5 and 4, and the upper hook-switch contacts to the left line, tip side of 
cord and running key to spring 3 on A relay, negative pole of battery B, 
through battery to positive pole of pole changer, 200w; resistance, springs 
9 and 8 of A relay, winding of A relay, two outside springs on sleeve side 
of running key, batteries C and D to ground. Relay A therefore oper¬ 
ates and is held up as long as the running key is closed; the holding cir¬ 
cuit may be traced from battery C, and two outer contacts on running 
key, A relay winding, springs 8 and 10 and back through the battery C, 



Fig. 272. (Selector. ) Fig. 273. 

The contacts between springs 3 and 4 and springs 6 and 7, now being 
open, the passing current is cut off from the line, and both ringer and 
relay armatures return to their normal positions. The closing of the 
contacts between springs 3 and 2 and springs 5 and 6 of A relay has at 
the same time established a circuit from the positive pole of main bat¬ 
tery, springs 2 and 3 of A relay, outside tip contacts of running key, over 
the tip and external circuit through the station, back over sleeve, running 
key, springs 6 and 5 of A relay, lOOw winding of relay C and through the 
normally closed contact of C relay to negative side of main battery. Cur¬ 
rent therefore flows through the station in ringing direction and unlatches 
the ringer, placing the subscriber in talking connection with the line. 
On releasing the running key the relay A drops back to normal, as its 












































SELECTIVE AND LOCK OUT SYSTEM 


205 


holding circuit is broken by the opening of the contact between the two 
outer springs on sleeve side of running key. The operator then sets up 
the required connection. 

29 Restoring the Line. —When the operator is notified by the super¬ 
visory signal that the party has hung up, she presses the passing key. 
This sends passing current through his instrument, and latches up the 
ringer, his talking circuit being thus restored to its normal, or locked out 
condition. She then throws over the running key, and (assuming that 
there are no more signals to pick up), the selecting relays are successive¬ 
ly operated to the end of the line, and finally the grounder is unlatched. 
As previously explained in Par. 18 the left line is thus grounded through 
the winding a and springs 1 and 2, the contact between springs 3 and 4 
being broken. As previously explained in Par. 28 this grounding of the 
left line causes the operation of the central relay A which cuts off the 
passing current and applies ringing current across the line. Since, how¬ 
ever, the grounder circuit is open at springs 3 and 4, no ringing current 
flows out over the metallic line, and the lOOw winding of the central relay 
C, which is included in this circuit is not energized. A circuit may now 
be traced from the ground through the grounder winding a over the left 
line, tip, running key, springs 3 and 1 of relay A, the 1500w winding of 
the relay C, batteries C and D to ground. As the lOOw winding of the 
relay C is not energized, its centrally pivoted armature is operated by 
the 1500w winding and closes the ground contact. Restoring current 
now flows from ground through the armature of C relay, negative pole 
of main battery, through main battery, springs 2 and 3 of A relay, tip 
side of running key over tip and the left line, through the coils D of the 
selecting relays, and the grounder winding a to ground; as previously 
explained this restores the selecting relays and the grounder to normal 
condition. 

30 Selecting a Given Party. —Suppose No. 4 is the station called 
for. To set the selector the operator takes hold of the handle to which 
is rigidly attached the pointer P and the arm carrying the pin F, the 
whole being free to rotate on the main shaft of the device, placing the 
pointer P at the given number 4. On pressing the handle the pin F en¬ 
ters one of the slots of the setting wheel S and the operator then turns 
the pointer back to o. When in this set condition spring 6 is raised out 
of contact with spring 5 by the tip of the arm A. The latter in its back¬ 
ward rotation when being set also carried with it the setting wheel S 
and the ratchet wheel R, to which is fixed the rubber pin C; the pressure 
of the latter on the spring 3 is therefore removed and spring 3 rises into 
contact with spring 4, spring 1 also contacting with spring 2. If the 
operator now closes the ringing key, the escapement o ’ the selector will be 
actuated by its magnet, current flowing in a local circuit rom the ± pole 
of pole changer through the two outer springs on the tip side of the ring¬ 
ing key, magnet M, springs 2 and 1 of selector and back to negative pole 
of pole changer. Under the influence of its coil spring the selector is 
rotated one notch, and spring 6 returns into contact with spring 5. This 
closes a circuit from the positive side of pole changer through springs 
5 and 6, 4 and 3 to sleeve, out over the external circuit, back to tip and 
through the ringing key contacts to the ± pole of pole changer. The 
passing impulses thus sent out over the circuit from the -f- side of the 
pole changer operate the selecting relays out on the line, the negative im¬ 
pulses operating the escapment of the selecting device. When the pole 





206 


TELEPHONOLOGY 


changer has sent out 3 passing impulses, the next negative impulse re¬ 
leases the final tooth of the selector, which brings the latter back to its 
normal position. 

31 The contacts 3 and 4 now being open no more passing impulses 
are sent to line, but through contacts 3 and 1 the selector automatically 
reverses the circuit, thus sending ringing impulses to line. The local cir¬ 
cuit of the selector magnet is also broken between springs 2 and 1. Since 
three passing impulses have been sent to line the relays at station 1, 2 
and 3 have been operated and station 4 placed in circuit. The ringing 
circuit may now be traced from the rfc pole of the pole changer through 
ringing key and left side of line and back over sleeve, through ringing 
key outside spring, springs 3 and 1 of selector to negative pole of pole 
changer. To ring a second time it is unnecessary again to set the selector 
before pressing the ringing key. 

32 If desired, the passing key may be used to select a given station 
in place of the selector. It will be noted that pressing the passing key 
simply places the main battery B across the line in passing direction 
which will operate the relay at station 1. After pressing the passing 
key three times the circuit will be extended to No. 4 and the bell at that 
station may be rung with the ringing key. The dial selector is used sim¬ 
ply to save time and ensure accuracy in the selection of high numbers. 

33 The Restoring Key. —When the restoring key is operated the 
main battery is bridged between the tip side of line and ground. As 
previously explained in Par. 17, this restores to normal whatever select¬ 
ing relays have been latched past. Besides being employed in connect- 
the line between central and the seat of trouble if such exists on the line. 
If she is unable to restore the line by the usual means, which would be 
the case in the event of an open circuit or short on the line, she can do so 
with the restoring key. Hence, in case of trouble that prevents the oper¬ 
ation of the line beyond a certain station, the seat of trouble is revealed 
at or just beyond that station. 

34 Line Control. —It will be noted from the description so far given 
that the proper operation of the bells and relays on the line does not de¬ 
pend on any contacts under the control of the subscriber, who is at all 
times unable to prevent the operator from handling the line as she sees 
fit. The bell may be rung with the hook up or down. 

35 Looping In. —It is evident from the description so far given that 
it is necessary to lead the two main line wires through the subscriber’s 
station, i. e., there are four wires at each telephone, two in and two out. 
To save the expense of running two pairs of wires from the main line in 
cases where the telephone is situated at some considerable distance, the 
selecting relay may be placed at the junction with the main line, in which 
case a slight modification of the wiring, and the addition of another con¬ 
denser, obviates the running of more than two wires to the subscriber’s 
station. Fig. 273 shows the arrangement of the circuit where the select¬ 
ing relay is placed on the junction pole. 

By a slight change in the instrument circuit, this system may be 
used with a common talking battery. 

Some special tests for the location of line troubles are possible with 
this system. These are as follows: 

Measuring Resistance. —If the exchange is not provided with a 
bridge testing set, a high resistance dead beat volt meter with double 
scale (3 volts and 150 volts) will be found very convenient for this pur- 




SELECTIVE AND LOCK OUT SYSTEM 


207 


pose, in any case a volt meter should be used when testing ground resist 
ance at the substations. To measure a resistance with voltmeter use the 
3 volt scale, and connect the voltmeter directly in series with two new 
dry cells. If the deflection is over 150 measure the deflection for each 
cell separately and add the two together. Suppose the total deflection 
is 148. Now connect the unknown resistance in series and again note 
the deflection. Suppose it is 65. The resistance of the 3 volt winding of 
the voltmeter, which must of course be known previously, we will suppose 
is 205 ohms. We can now calculate the resistance by the following rule: 
Multiply the resistance of the voltmeter by the difference between the two 
deflections and divide the product by the second deflection. 

205 X 83 

Thus - = 262 ohms. 

65 

Measuring External Resistances .— (a) To measure the end instru¬ 
ment ground resistance. Instruct the operator to select past the end of 
the line and unlatch the grounder, thus putting a ground on left. Take 
out the fuses or heat coils at central and then measure the resistance be¬ 
tween left and the central office ground. Suppose that there are 10 in¬ 
struments on the line, and the line is No. 12 iron 7 miles long, and the 
total resistance measures 680 ohms. The resistance of the low winding of 
the grounder is about 125 ohms, and the series windings in left have a 
resistance of about 20 ohms, the line resistance being about 35 ohms per 
mile = 245 ohms. The total known resistance is thus 125 -f 200 -f- 245 
= 570 ohms; the ground resistance is therefore 110 ohms. 

(b) To test the insulation resistance between left and right, un¬ 
latch the grounder as before; this opens the metallic circuit between left 
and right. 

<c) To measure the total line resistance select the end phone with¬ 
out ringing the bell, the line resistance will then be the total resistance 
less the phone resistance (1000 ohms approx). The line resistance thus 
determined includes the resistance of all the series windings of the selec¬ 
ting relays, (about 45 ohms per station, left winding 20 and right wind¬ 
ing 25). 

(d) To measure the substation ground resistance, instruct the opera¬ 
tor to ring the proper station, then remove the fuses, and connect the volt¬ 
meter alone between left and the central office ground. The deflection 
noted is caused by the local cells in the telephone; when a station has been 
rung on, the local cells are connected in series with the transmitter and 
primary between the left line and ground, (when the receiver is on the 
hook). 

These cells, however, may be run down to some extent and to be able 
to determine the deflection caused by the standard cells, insert them in 
series in the circuit so as to make them oppose the other pair in the 
phone. The terminals of the voltmeter must of course, be reversed. If 
the two local cells were not run down much, there will be little deflection 
of the voltmeter. 

Suppose the original deflection was 48 and the second reading noted 
is 7. Obviously, if the two standard cells had been in the circuit in place 




20K 


TV LK PHONOLOGY 


of the local phono colls when taking the first reading, the deflection would 
have been 4K | 7 55. The external resistance is 

205 X 93 

Thus - = 346 ohms. 

65 

To find the not ground resistance, subtract from this figure the resistance 
of the transmitter and primary (about 40 ohms) and the resistance of 
the loft lino and series windings up to the station being tested. 

Voltafje of Local l Celia.— (q) From the readings taken in the pre¬ 
vious case the condition of the local telephone cells may be readily esti¬ 
mated by comparison. Thus, if two now cells would have given a read¬ 
ing of 55 and the second reading was 7, the percentage loss in volts since 
the colls wore installed is 


1/7 X 100 

- 12.7 % 

65 

Localinf) Partial Grounda Willi Voltmeter .—First determine whether 
ground is on left or on right. To do this pass to the end of the line with¬ 
out unlatching grounder, remove fuses and then test resistance between 
ground and each side of line. Suppose ground is on left. Instruct oper¬ 
ator to restore line to normal. Again remove fuses and measure the re¬ 
sistance between right and ground. Then have the operator pass sta¬ 
tion I and test again. Assuming that the ground is beyond the second 
station, the ground resistance should now be about 5 ohms greater owing 
to I he fact that the right line series winding at station 2 has been placed 
in the circuit instead of the loft lint* series winding. If the total ground 
resistance is high il is possible that the difference in the voltmeter read¬ 
ing can be hardly noticed, and therefore the voltmeter should be read as 
accurately as possible. If the next station bo passed and the test repeat¬ 
ed, the resistance will increase 1 another 5 ohms, and so on down the line 
until the ground is reached. As soon, however, as the station beyond 
the ground is placed in circuit the resistance will suddenly increase by at 
least 25 ohms, since the test current must pass over the richt line to the 
station beyond the ground, and after crossing over to the left line through 
that station must then return oyer the left lira' to the source o ' trouble. 

The location of a ground on the right dine may be determined in a 
similar manner, in this case, however, test the resistance from left to 
ground. The resistance instead of increasing will decrease 5 ohms for 
each step until the ground is reached, when the resistance will show a 
sudden increase of 30 ohms or more. 

An easier way of locating a ground on right is to test the resistance 
from right to ground instead of from left to ground and step down the 
line as before described, before the ground is reached, the test current 
must pass from right lint* across to left and then from left back across 
to right through the station just beyond the ground. Thus, as soon as 
all the stations between central and the ground are passed, the resistance 
between right and ground will then decrease by about 2000 ohms, as the 
test current will go din'd over right to ground. 




CHAPTER VII. 


BATTERIES. 


If a piece of zinc and one of carbon are immersed in the proper solu¬ 
tion and connected together with a wire, a current will flow from one to 
the other. When this occurs, the zinc will be eaten up by the solution 
with more or less rapidity. Other substances besides zinc and carbon 
may be used, but these are the substances in common'use. 

The simple cell as alluded to above is shown in Fig. 274. Here it 
will be seen that the current flows from the zinc through the liquid to 
the carbon, while outside of the liquid the current flows from the carbon 
to the zinc. The zinc is termed a minus-electrode, while the carbon is 
termed a plus-electrode. If the carbon and zinc are not connected by a 
wire, no current will flow, and the zinc will be very slowly consumed; the 
cricuit would then be termed “broken” or “open.” The term “open circuit” 
battery is applied to any form of battery not intended for continuous 
work, when the circuit is “open” most of the time. In other words, an 
“open circuit” battery is intended for intermittent use, such as that in 
an ordinary telephone, while for a switchboard which is continually in 
use, what is known as “closed circuit” batteries are used.- 



Fig. 274. Fig. 275. 


The part of the circuit outside of the batteries connecting the two 
poles or electrodes, is termed the external circuit, while the circuit 
through the liquid of the cell is termed the internal circuit. 

The internal resistance of the battery is the resistance which the 
battery offers to the passage of a current through it. 

The current given by a battery is equal to its electro motive force or 
voltage, divided by the external and internal resistances added together. 

For instance: if three cells giving two volts each are placed in 
series so that they give a total of six volts, and the internal resistance of 

(209) 


1 4 























210 


TELE PHONOLOGY 


each cell is one ohm, making a total of three ohms for the entire battery, 
and the external resistance, or the resistance inserted between the wires 
connecting the two outside terminals of the three cells equals three ohms, 
then the current flowing will be six volts divided by three ohms internal 
resistance, plus three ohms external resistance, the result being one 
ampere. 

The internal resistance of a battery for telephone work should be as 
low as possible, and the chemicals should destroy the gas which collects 
on the negative electrode as soon as formed. 

When the battery becomes inoperative, due to the collection of gas 
at the negative plate, it is said to be polarized. This is prevented in the 
sal ammoniac battery, shown in Fig. 275 by the addition of a substance 
called peroxide of manganese, which is formed into bricks and placed 
around the carbon. This chemically unites with the gas formed in the 
cell, disposing of same. The same action is secured by making the car¬ 
bon electrode much larger than the zinc. 

The sal ammoniac battery polarizes very quickly, but when given a 
rest it just as quickly recovers. This cell is there ore fairly well suited 
for telephone use, but is now almost universally supplanted by the dry 
battery. A standard dry battery is shown in Fig. 276. There are many 
shapes and sizes, but the general construction and details are the same. 

The outside or containing vessel consists of a sheet of zinc of suita¬ 
ble form, with a zinc bottom. This is lined with blotting paper. A piece 
of carbon is placed in the centre of the cell. The blotting paper is satu¬ 
rated with a chemical solution, and the space between the blotting paper 
and carbon is filled to with a mixture of powdered carbon and manganese. 
The battery is filled to within one inch of the top with this mixture; the 
remaining space is filled with asphaltum, or a substance resembling seab 
ing wax, and the battery is ready for use. 

Dry batteries give 1 1/2 volts per cell, and deliver on a short circuit 
from 15 to 20 amperes. 

The use of batteries of exceedingly high amperage should usually 
be avoided in telephone work, and it is generally found that batteries 
delivering a very high initial current do not possess lasting qualities, and 
consequently those possessing a reasonable amount of amperage are more 
satisfactory for telephone work, as a great quantity of current is not 
desired, while long life is necessary. 

There is absolutely nothing to be gained by making dry batteries 
at home, as the cost of the raw material and labor will amount to double 
what a cell is sold for, in addition to which commercial batteries will be 
found more satisfactory in every way; but as an illustration of the pro¬ 
cess of making dry batteries and for those who desire to experiment 
along this line, the following method is given: 

A form should be made of hard wood of the dimensions desired. 
Some sheet zinc, No. 10 or 11 gauge should be wrapped around the form 
and cut to fit, allowing 14 , inch lap to form the seam. Solder, taking 
care not to get any solder on the inside of the can. 

The best solution for soldering zinc is muriatic acid in which is dis¬ 
solved all the zinc possible. Take one ounce of muriatic acid and add a 
few scraps of zinc; as soon as the solution stops gassing it can be used. 
Apply to the zinc by means of a small stick or rag, and solder with a 
clean hot iron. 


BATTERIES 


211 


Place the can on a piece of the zinc, and mark around on the inside 
of the can; cut this out to form the bottom of the can, making a snug 
fit. Solder the bottom in the can about 1/8 inch from the edge. 

A card board lining should now be made. Cut a piece of card board 
or blotting paper that will fit tightly in the bottom of the can, then line 
the can taking care that there are no bare places left, and allowing a 1 / 4 , 
inch lap. Have the lining come entirely to the top of the can. A bind¬ 
ing post can be soldered to the can, which forms the zinc or negative ele¬ 
ment of the battery. 

The positive pole consists of an ordinary stick of carbon, such as is 
used in arc lamps or a carbon from an old dry cell can be used if first 
boiled in water and allowed to dry. If electric light carbon is used a 
piece should be selected about 6 1/2 inches long, or long enough to project 
1/2 inch above the top of the can. The top of the rod should be filed flat 
on two sides, and a binding post attached, by boring a hole through the 
carbon and using a machine screw with washer. Soak the end of the 
carbon to which the binding post is attached in paraffine. 



Fig. 276. 


S CAL/HCr C OS* POua/o 

2//VC POST 


pAPfR L /S//A/6- 
2 . /S/C CA/V 



CA 


CA/V 

RBOAf^ \ 



• ' 

-.-.-r-rT' 


7^> woe hep 
car 


LAVCRf, 
OR i //V//VG- 


Fig. 277. 


The chemicals required are powdered carbon, peroxide of mangan¬ 
ese and chloride of zinc. The powdered carbon and manganese can be 
purchased for five or ten cents a pound. The chloride of zinc should be 
in powdered form, and costs from twelve to fifteen cents. If a small 
quantity only of the powdered carbon is desired, take some electric light 
carbon and break it up into small fragments. These can be powdered 
up and used with good results. 

Make a solution of the chloride of zinc: take four ounces of water 
and put in it all the chloride that will dissolve; add to this 1 1/2 ounces 
of water; then add two or three tablespoons full of sal ammoniac. Suffi¬ 
cient of this solution should be poured into the can to thoroughly saturate 
the blotting paper. The can should then be turned upside down and 
the surplus solution allowed to run out. 

The carbon rod is then held in the middle of the cell, while a mixture 
of equal parts carbon powder and manganese, which has been sprinkled 








































212 


TELEPHONOLOGY 


with some of the solution used to saturate the blotting paper, is tightly 
packed around the carbon. The tighter this packing is, the better the bat¬ 
teries will be. Great care should be taken not to break through the lining 
and that none of the black powder comes in contact with the zinc can, as 
this will render the batteries worthless. Fill the batteries with the mix¬ 
ture until within Vi" of the top. 

Now shake out any loose carbon which may be on top, and carefully 
turn down the blotting paper all around. Take care the blotting paper 
does not touch the carbon, as this would be fatal. The blotting paper 
should be at least % inch away from the carbon all round, and the 
blotting paper should be clean. It should not have any black crumbs on 
top of the paper to come between it and the zinc. After turning down 
the paper, fill the batteries with sealing wax level with the top of the 
cell. 

The complete cell and method of assembling same are shown in Fig. 
277. Most of the materials can be obtained from old batteries. A little 
experimenting to get the best solution will be necessary to get good re¬ 
sults. 

As previously stated, there is nothing to be gained by making dry 
batteries except that it will afford an opportunity for experiment, and 
in cases of necessity, such as when a special shaped cell is desired, it is 
sometimes convenient to know how to make them. 

Dry batteries are of the open circuit type, and should never be used 
for switchboards or other heavy service where they are constantly in 
use, as they will soon fail and once exhausted are practically worthless. 

Dry batteries may be temporarily renewed by drilling a few holes 
through the outside case and setting the batteries in a jar filled with a 
strong solution of sal ammoniac. This serves very well in an emergency 
case where it is necessary to get a telephone in working order quickly. 
In case no sal ammoniac is at hand, a strong solution of salt and water 
may be used. Do not punch the holes in such a manner that the zinc 
case is forced through the paper lining. Cut the holes clean, using a 
hand drill and Vs in* drill. 

As dry batteries are principally used in telephones on rural country 
lines, it is well to caution our farmer friends not to leave their receivers 
oft the hook, and it is well to caution them against half hour conversa¬ 
tions, which are not at all conducive to the building up of the strength 
of the battery. 

On farmers’ lines, where each subscriber pays for the maintenance 
of his instrument, it is well to instruct the person using the telephone 
how to replace the batteries in case some become exhausted, particularly 
to connect the carbon on one cell to the zinc of the other and then con¬ 
nect the two remaining posts to the wires provided for this purpose in 
the telephone instrument. This is a very simple process, and if the sub¬ 
scribers are instructed to do this, it will very often save the exchange 
manager a long drive in the country and the attendant trouble and ex¬ 
pense. 

Another form of cell known as the “Fuller” is often used in long 
distance service. For a number of years the Bell companies used two 
of these cells in connection with each long distance instrument. They 
give highly satisfactory results. The complete cell is shown in Fig. 278. 

The negative electrode consists of a heavy piece of zinc in the shape 
of a cone, to which is connected a heavy copper wire. The positive elec- 



BATTERIES 


213 


trode is a flat carbon plate. The jar is provided with a wooden cover. 
A porus cup is provided in which the zinc is placed. The solution for 
use in this battery is as follows: 


Sodium Bi Chromate. 6 oz. 

Sulphuric Acid.17 oz. 

Soft Water.56 oz. 


The Sodium Bi Chromate should be powdered and dissolved in the 
water. Then add the acid slowly. Never pour the water into the acid 
and be careful not to let any of the acid get on the clothes or in the eyes. 
The mixture will become very warm, and should be made in an earthen 
ware vessel and not in glass, as glass is liable to crack. If the Sodium 
Bi Chromate is not obtainable, Bi Chromate of Potash may be used. 



Fig. 278. Fig. 279. 


The porous cup should be placed in the centre of the glass jar, and 
the space outside the porous cup filled with the solution until it reaches 
within one inch of the top of the cup. A teaspoonful of mercury together 
with the zinc is placed in the porous cup, which is then filled with water, 
to which is added two teaspoonfuls of common salt. Bring the wire 
from the zinc up throue-h the hole in the centre of the wooden cover and 
put same in place. The carbon is then lowered through the slot, and 
the cell is ready for use. 

The jars are about 6 inches in diameter, and 8 inches in depth, and 
the carbon plates are 4 inches wide, about 8 inches long and Vi inch 
thick. 

Be'ore putting the zinc in place, it and the wire should be amalga¬ 
mated by rubbing with sulphuric acid and mercury, so that the bare 
copper is not exposed to the solution. This prevents the copper from 
being eaten away. 

The Fuller cell gives a little over two volts. Two o" these are used 
in connection with a telephone instrument. The current from one cell 
is eight amperes. For switchboard work three of these cells may be 
used, and give good results. 






































































214 


TELEPHONOLOGY 


The carbon plate seldom needs renewing, but the zinc will be gradu¬ 
ally eaten away. When the solution becomes almost black the cell is 
exhausted and the solution should be thrown away. By re-amalgamating 
the zinc and adding new solution, the battery is again ready for use. 

Sometimes the action of the cell can be temporarily renewed by 
stirring the solution and adding a little water. 

Clean carbons, when renewing cells, by scrubbing them with hot 
water and sand. Remove all the white accumulation before replacing. 

Another variety of cell known as the “Gravity,” “Crow foot,” or 
“Bluestone ” battery is shown in Fig. 279. This battery is widely used in 
telephone work, and is suitable where a small but constant current is 
required. This cell possesses a very high internal resistance, and for this 
reason is not a very efficient battery, but owing to its long life, cheapness, 
and ease of setting up, it is often used in connection with operator’s 
transmitters on small magneto switchboards. 

The positive electrode consists of three sheets of copper fastened to¬ 
gether at the middle. To this is attached an insulated wire. The zinc 
is in the form of a crow foot, with a lug by which it is suspended from 
the edge of the jar. 

The batteries are set up by first unfolding the copper and placing 
same in jar, as shown in the illustration. Sulphate of copper, or as it 
is commonly called, “blue stone,” is then put in the jar to a sufficient 
depth to cover the copper. The blue stone should be clean and free from 
lumps. It is well to wash it thoroughly before putting it in the jar. The 
jar is then filled with water until the zinc is covered about V 2 inch. The 
wire from the copper should be bent in a sharp loop at the edge of the jar 
to keep the copper in place and immediately attached to the zinc for ten 
or fifteen hours before the battery is desired for use. 

If the battery is desired for immediate use, a teaspoonful of sulphu¬ 
ric acid may be added to the solution, or teaspoonful of common salt. Do 
not do this if it can be avoided. 

The solution attacks the zinc and produces zinc sulphate. This is a 
colorless fluid lighter than the copper sulphate which is formed at the 
bottom of the cell. The dividing line between the two solutions should 
be half way between the top of the copper and the bottom of the zinc. 
The dividing line may be easily detected, one solution being a deep blue, 
the other almost colorless. This accounts for the name, “Gravity Bat¬ 
tery,” as gravity keeps the solutions apart. The dividing line between 
the two solutions is termed the “blue line.” 

If the blue solution rises too high in the cell, some of it may be drawn 
off by inserting a rubber tube or siphon to the bottom of the cell. The 
amount of the solution withdrawn should be replaced by adding water 
on top. If the battery is in constant use, the blue rises upwards. The 
reverse is usually the case, however, in which case ^ome of the sulphate 
from the top of the cell should be taken out and replaced by clear water. 

Before setting up the battery the top of the jar should be wiped off, 
and when the zinc becomes so corroded that it represents a black appear¬ 
ance and large accumulations of crystals appear, it should be taken out 
and cleaned. The lumps can be removed by striking them with a hatchet. 
Wash well before replacing. 

The copper will not need any attention. Occasionally a few more 
crystals of the blue stone may be dropped in the battery. 







BATTERIES 


215 


A wooden top can be cut to fit the batteries, and this will prevent 
evaporation to a considerable extent. This can be held in place by tying 
a piece of tape around the crack between the top and the jar, which will 
effectually exclude the air. Varnish this top with Shellac or Asphaltum. 

When renewing batteries, save the top solution from the old cells 
and put it in the new ones. This will start the chemical action immediate¬ 
ly, and it will not be necessary to short circuit the cells and wait for the 
action to take place. 

A gravity battery gives very nearly one volt. The internal resist¬ 
ance is much higher than other types, but the cells are easy to set up, 
eosl little to maintain, and with proper care will run from six to eight 
months without a complete renewal. 

Three cells are sufficient for the operator’s transmitter on magneto 
switchboards and it is better to keep the transmitter always in circuit, 
as a small but constant flow of current keeps the battery in better condi ¬ 
tion than if it is left open circuit part of the time. 

A very successful method of making comparative tests of batteries 
is shown in Fig. 280. The relay can be made from a pair of ringer spools 
wound to a resistance of about 50 ohms, or a pair of 80 ohm ringer coils 
will do. 



The armature A is constructed as shown, and is normally held up by 
a rubber band. Contact springs, S may be made from old hook springs 
so mounted that when the relay is operated, all the points will be closed 
together and a circuit formed from T through armature A to springs 
S, through the 20 ohm coils and back to Tl, T2, T3, etc. 

The Terminals CT should be connected on ordinary clock shown in 
Fig. 281 which is equipped with a pasteboard dial upon which is mounted 
three contact pieces of copper which occupy the positions shown in the 
figure. These pieces are connected together and form one side of a cir¬ 
cuit, the other side of which is formed by the clock body itsel . 

The minute hand is adjusted by bending so that it will contact on 
each copper piece in passing, thus closing the circuit for three periods 
of five minutes each, per hour. 
















































































216 


TELEPHONOLOGY 


To terminals RB, connect a battery of sufficient strength to properly 
operate the relay. A direct current electric light circuit may be used 
for this provided sufficient lamps are placed in circuit to prevent the re¬ 
lay from sparking. 

The Batteries under test are connected in pairs. The carbon side 
of all the pairs connect together and to T. The zinc side of each pair 
goes to Tl, T2, T3, etc. 

Push buttons as shown at Kl, K2, etc, as provided for testing the 
voltage of the different sets, using the voltmeter placed in circuit as 
shown. 

The clock is started and it will be seen that each set of batteries is 
short circuited through a resistance of 20 ohms (which represents the 
average resistance of a transmitter and Pri. coil) three times an hour 
for periods of five minutes each. 



The test;may be said to equal the use the batteries would get if 
placed in a telephone used three times per hour for five minutes each time. 

The voltage reading should be taken every day at the same time, and 
immediately before the clock circuit is closed or open. Always test for 
voltage under exactly the same conditions each time. 

When any set falls below 1 1/2 volts it is assumed the cells are unfit 
for service. By this method their life can be ascertained in a few weeks, 
instead of a year which would probably be necessary if an actual service 
test were made. 

Usually only two or three makes of battery will be tested at once, in 
which case only two or three springs are necessary on the relay. 

The clock may be allowed to run continuously or may be stopped at 
night. The latter method more nearly approximates service conditions. 

Fig. 282 shows a chart for recording the test. This also shows the 
record of a test of five groups of cells, from which it will be noted that 
quite a difference between different makes exists, set No. 1 having nearly 
twice the endurance of set No. 5. 

While this test is illustrated as applied to dry cells, any form of bat¬ 
tery may be tested in the same manner or two different types may be 
compared for relative efficiency. < 

In telephone work the series arrangement of cells is generally used, 
this is shown at A Fig. 283. 







BATTERIES 


217 


To find the voltage of a set of cells in series multiply the voltage of 
a single cell by the number of cells. This shows that an increase in volt¬ 
age is accomplished by putting the cells in series, but the quantity of 
current or amperes, remains the same. 

Sometimes a multiple arrangement is to be preferred, as shown at 
B Fig. 283. When it is necessary to temporarily use dry cells for an 
operator’s transmitter at switchboard, this arrangement will serve until 
the regular cells are recharged and will last much longer than if only 
two cells are used. With the multiple arrangement the quantity of cur¬ 
rent or amperes is increased, the voltage remaining the same as if only 
two cells were used. 


jjvOUTS 

TtST 

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24 

27 

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33 

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39 


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51 

54 

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CO 

63 

66 

69 

7i 

75 

78 

DAY 

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Fig. 282. 


To find the current and voltage given by a number of cells in multi¬ 
ple multiply the current of one cell by the number of cells, this gives the 
current (Amperes). The voltage will be that of as many cells as there 
are in series. For instance as shown in the figure, three sets of two cells 
each are used, and the voltage is that of two cells, the amperage that of 
6 cells. 

If three sets of three cells each were used the voltage would be that 
of three cells, while the amperage would be the same. 

One bad cell in a group of batteries will affect the current and volt¬ 
age of the entire group. This is because the internal resistance oc a cell 
increases as it becomes exhausted. The power of the good cells is there¬ 
fore used up in trying to force a current through it. It is therefore pool 
policy to use old and new cells together, as the old cells are liable to ren¬ 
der the combination useless. , 

A bad cell as shown at C in the figure will render the output of the 

three good cells practically nothing, care should therefore be taken to 
test batteries carefully for both voltage and amperage before connecting 
them up. Cold weather often affects the amperage of dry cells and allow¬ 
ance should be made for this when testing them After placing dry cells 
in a moderately warm room, the amperage will rise. The cold has n 

permanently bad effects. 









































































218 


TELEPHONOLOGY 


The wires used for connecting cells together should be sufficiently 
heavy to withstand handling, and to be of low resistance. No. 14 is a 
good size. This should be rubber covered. 

The use of spirals or pig tails in the wires connecting the cells 
should be avoided; while these look nice they introduce an extra and un¬ 
necessary resistance in the circuit. 

The method of attaching the wires to the cell binding posts should 
receive careful attention. At D Fig. 283 is shown the right way. When 
the nut is tightened, the tendency is to wrap the wire more tightly around 
the neck of the post. The wrong way is shown at E, when the nut is 
tightened it tends to unwrap the wire and thereby cause a loose connec¬ 
tion. 

When the type of binding post shown at F is used, the wire should be 
doubled and twisted as shown at G. The wrapping serves to hold the 
covering in place, and doubling the wire prevents it from being cut or 
broken by the screw in the binding post. A good form of connector for 
dry cells is shown at H. 



Fig. 283. 


In running wires from the batteries to the apparatus, never put 
both wires under the same tack or staple. Have the wiring as short as 
possible and free from splices, and when the battery is used for talking 
purposes and the wires parallel others for any distance, twist the battery 
wires together to eliminate any disturbance due to induction. 

Always put the batteries in a box or other receptacle, where they will 
be protected from dust and the connections from accidental breakage. 

The batteries for a switchboard should never be placed in the board, 
nor should the operator’s transmitter batteries be placed very far away, 
as the least resistance in the transmitter circuit, the better. Have every 
connection tight to avoid sputtering noises and loss of power. Look over 
the batteries at least once a month, and a great deal of trouble will be 
saved. 

Dry batteries should not be purchased and kept on hand, as they 
deteriorate with age. Do not secure them more than 30 days before they 
are needed for use, and be sure they are fresh, and just from the factory. 

The various batteries so far described are principally used in connec¬ 
tion with intermittent work, and with the exception of the gravity or 
blue stone, and the Fuller cells, should never be used when a constant cur¬ 
rent is required. When a constant flow of current is required, some form 
of closed circuit battery is necessary. There are several forms of closed 
circuit batteries on the market, these being of the caustic soda type using 
copper oxide and zinc elements. While these are suitable for use where 
constant current is desired, still for telephone purposes especially in con- 




















BATTERIES 


219 


nection with central energy or common battery exchanges, nothing but 
storage batteries should be used, and nothing but storage batteries have 
come into extended use for this work. 

As the storage battery reaches the exchange completely constructed, 
it is useless to enter into the deails of manufacture, except to state that 
the plats are formed from lead. The negative plate consists wholly of 
spongy lead, while the positive plate is lead peroxide—these are shown in 
Figs. 284-285. The positive plate is usually formed from a solid sheet of 
lead in which holes or ridges are punched or rolled, into these the material 
forming the plate is forced, the ridges holding the same in place. 




Positive. 


Fig. 284. 


Fig. 285. 


The solution used is pure sulphuric acid and water. Storage bat¬ 
teries give a current slightly over two volts each. It does not matter how 
large the cell is, voltage always remains the same. Increase in the size, 
however, increases the amperage. 

The storage battery is the same as an open circuit battery in opera¬ 
tion, except that after it is discharged it can again be recharged without 
the addition of any new material, or without changing the plates, by 
sending a current through it in the proper direction. 

The smaller types of storage cells have two plates, while in the larger 
cells several positive and negative plates are used. Where there are more 
than two plates in one cell, there is always one more negative than posi¬ 
tive plate, the arrangement being such that one positive is placed be¬ 
tween two negatives. 

Four small storage cells are shown in I 1 ig. 286. When the cells are 
received from the manufacturer they should be carefully unpacked, an 
any excelsior or other foreign substance removed from the plates and the 
jars carefully cleaned. The manufacturer usually furnishes complete 
directions for setting up the battery and giving the initial charge, which 
varies with the different makes. The directions accompanying each bat¬ 
tery should be rigidly adhered to. 

The best method of connecting cells is to permanently join the ter¬ 
minals by burning the lugs together. In small cells this is not necessary, 
as bolts are provided by means of which the terminals can be properly 
connected. Nothing but lead bolts should be used for this purpose; brass 






























220 


TELEPHONOLOGY 


and iron bolts will corrode and cause local action. The smaller cells are 
set up with the plates in pairs as shown, which renders all connections 
unnecessary. 

Each cell should be placed on a wooden base painted with insulating 
paint and should rest on glass or porcelain insulators as shown in Fig. 
287. The cells should be placed near a window or other opening so that 
the gas, which escapes when charging, will have an outlet. Fig. 288 
shows how cells are usually mounted. 

After the cells are set up the electrolyte should be added. It is im¬ 
portant that this should not be put in the jars until just before the cur¬ 
rent is turned on. 



Fig. 286. 



Fig. 287. 


If possible the electrolyte should be procured ready mixed from the 
manufacturer of the batteries, but if this is impossible, a mixture of pure 
sulphuric acid and water should be used. This should have a specific 
gravity of 1.200 on the ordinary hydrometer scale, or 23 Baume scale. 

A hydrometer is a small glass tube like a thermometer, weighted at 
one end. The depth to which it sinks when placed in any liquid is shown 
on a scale and denotes the density of the liquid. 

The mixture should be made in a large porcelain crock as it will 
become hot and a glass vessel is liable to crack. It is best to prepare the 
electrolyte several hours before use as it must be perfectly cool before 
using. The vessel should be absolutely free from any dust or metallic 
substances. Stir the mixture with a stick. 

The charging current must be a direct current, and the positive pole 
of the battery must be connected to the positive pole of the generator. This 
can be ascertained with a voltmeter of the permanent magnet type, or by 
dipping the ends of the charging wires in a glass of electrolyte, where, if 
they are separated about Vk" small bubbles of gas will collect around each 
wire. The negative wire will gas more freely than the positive. The po¬ 
larity of the charging current must be definitely determined before con¬ 
necting same to the batteries, for if the charging current is reversed, it 
will ruin the cells. 

After covering the plates about V 2 " with the solution the charging 
current should be turned on. The amount used, length of charge, etc., 
vary according to the size of the battery, but it should be borne in mind 
















BATTERIES 


221 


that the initial charge should be as continuous as possible: that is, after 
once starting the charge it should be continued to the end. Provision 
should be made to accomplish this if possible, if not, it will take a great 
deal longer to charge. During the last hours of the first charge the solu¬ 
tion will apparently boil and the specific gravity rise. If above the figures 
given by the maker, water should be added, while, if the specific gravity 
does not exceed the given point, some diluted sulphuric acid of specific 
gravity of 1,400 should be added. It is well in giving the initial charge to 
slightly over-charge the batteries. 



Storage batteries can be charged by means of any direct current 
lighting circuit by connecting lamps, as shown in Fig. 289, which shows 
a small cell. The arrangement is the same for any size battery except 
more lamps are used. In the case of a 110 volt circuit, each lamp may be 
rated as allowed 1 / 2 " ampere to pass. Therefore if the normal charging 



Fig. 289. 


rate is 3 amperes, 6 lamps arranged as shown, should be turned on, which 
will allow 3 amperes to flow through the batteries. It is safe to asseit 
that the charge should be continued at the normal rate until there is no 
more rise for one-half hour either in the voltage or specific gravity of the 
cells. The charging should be done often enough to prevent the voltage 

























































































































































222 


TELEPHONOLOGY 


of the cells from dropping below 1 8-10 volts per cell. Never allow the 
battery to stand completely discharged, or repeated overcharging will be 
necessary to bring the cells up to normal voltage again. 

Every two weeks charging should be continued two hours longer 
than is necessary to reach the maximum voltage and specific gravity. 

The specific gravity is a more reliable indication of the state of the 
charge than is the voltage. If the specific gravity is made uniform for 
all cells when fully charged, tests made on one cell will be sufficient for 
the specific gravity, as well as the voltage of the entire battery. 

For the sake of uniformity, the specific gravity should be read at a 
temperature of 70 deg. F., and should be made 1.200 or some number 
slightly in excess of this. Allowing for fluctuations due to variations in 
temperature, the specific gravity should not be below 1.195 nor above 
1.215. Heat will lessen the specific gravity, while cold will raise it. Any 
changes beyond the ranges given by the manufacturers are indications 
of faults. 

Use water and not acid to replace loss of solution due to evaporation, 
and under no circumstances allow the electrolyte to fall below the tops 
of the plates. 

Observations of the specific gravity should be taken at the begin¬ 
ning and at the completion of the charge. The specific gravity and volt¬ 
age of each cell in the battery should be observed at least once every 
week, at the end of the charge, with the charging current on. Each cell 
should read 2.5 volts when fully charged. 

The boiling of the electrolyte causes a fine spray to arise. This 
loss should be replaced by water, and two or three times a year it may be 
necessary to add a little acid. This may be done by mixing the acid to 
the same specific gravity as the solution, and adding sufficient to keep the 
fluid level at the proper point. Never put undiluted acid in a cell, and 
if for any reason the purity of the acid is in doubt, it should be careful¬ 
ly tested. 

*“The impurities which are most likely to be in the acid and for 
which tests may be readily made are: Chloride or free chlorine, the 
salts of iron, copper, mercury, and the nitrates. Particular care should 
be given to the securing of assurance of the manufacturers, that the acid 
is manufactured from pure sulphur and not from iron pyrites. 

“The tests for chlorine or chlorides is made by taking a test tube 
partially filled with electrolyte and dropping into it a few drops of solu¬ 
tion of nitrate of silver. If chlorine or its salts are present a curdy white 
precipitate of silver chloride will appear. This chloride turns to a violet 
tint on exposure to light. If the clear liquid be poured off this white 
precipitate and strong ammonia be poured on it, it will dissolve. 

“Test for iron: The presence of ferrous salts in the electrolyte is 
shown if a dark blue precipitate falls down upon the addition of a solu¬ 
tion of prussiate of potassium. If ferric salts are present in the electro¬ 
lyte, a solution of yellow prussiate of potassium will give a blue tint. 
Consequently, if in two test tubes, one of which contains a few drops of 
yellow prussiate and the other a few drops of red prussiate, a little elec¬ 
trolyte be poured, the two tests can be made at once. If the impurities 
be present in small quantities there will not be a precipitate formed, but 
a bluish-green coloration will result. 


‘"American Telephone Journal. 









BATTERIES 


223 


“To test for copper, place a small quantity of electrolyte in a test 
tube and add an excess of strong ammonia. If copper is present a bright 
bluish tint will be given to the mixture. If in large quantities a choco¬ 
late-colored precipitate will be formed upon the addition of a solution 
of yellow prussiate of potassium. 

“If mercury is present, the mercurous salts will give an olive-green 
precipitate with iodide of potassium. To test for nitrates, some dipheny- 
lamine should be dissolved in a small quantity of concentrated, chemically 
pure, sulphuric acid and placed in a test tube. A small quantity of elec¬ 
trolyte is then dropped carefully in the same tube. If a blue color results, 
nitrates are present. Traces of nitrates are very objectionable, as they 
cause a suprisingly rapid deterioration of the plates.” 

In the mixing of electrolyte none other than distilled water should 
be used. 

It is best to charge the batteries during the time of the greatest 
load. The specific gravity of the elctrolyte will rise rapidly when nearing 
the completion of the charge. The normal point of this and the voltage 
will, however, be learned by experience, so that any abnormal gain in 
the cell will be quickly noted. 

The plates should be closely watched to see that they do not curl out 
of shape thereby short circuiting each other. If any of the cells should 
show marked difference in specific gravity or voltage, see if any sub¬ 
stance has fallen between the plates. If so, it should be removed with a 
stick or glass rod. 

A cell that has been short circuited will require an extra amount 
of charging after the trouble has been removed, by changing it separate¬ 
ly from the others. 

The color of the plates is a valuable indication as to the condition 
of the cells. The negative plates have a light slate color, while the posi¬ 
tive plates are a dark chocolate brown. Lightness of color is an indica¬ 
tion of insufficient charge. White coating on the plates will seriously 
interfere with the action of the cells, and should be removed by over¬ 
charging and discharging two or three times or by continuing the charge 
at one half the normal rate for two or three hours after the batteries are 
fully charged. Sometimes when batteries are put into service a white 
deposit will accumulate on the plates. This will disappear after a few 
repeated overcharges and should not cause any alarm. 

At least 80 per cent, of the energy in a good storage cell is obtained 
before the voltage falls below 1-9-10 volts. The discharge should never 
be carried below 1-8-10 volts. Never under any circumstances allow the 
battery to become completely exhausted. If it is allowed to stand in a 
completely discharged condition for two or three days, it will be seen that 
the capacity of the cells will be materially lessened, and repeated over¬ 
charges will be necessary to restore them to their normal condition. 

If for any reason it becomes necessary to move the batteries or take 
them out of service, they should be charged fully, and the acid should be 
siphoned out of the jars. The cells should then be immediately refilled 
with clear water, and discharged at the normal rate until each cell shows 
less than one volt. The plates should be removed and allowed to dry, 
and the acid can be stored for use until the cells are again set up. 

Suitable testing equipment should always be on hand. A double scale 
voltmeter reading to 3 volts on one scale and of sufficient range on the 







224 


TELEPHONOLOGY 


other for reading the entire voltage of the battery, together with a Hy¬ 
drometer reading from 1.15 to 1.25, a glass rod for working about the 
plates, and a battery lamp for the purpose of examining the plates is 
very desirable. 

For large systems it is well to prepare a charge record sheet, as 
shown in Fig. 290. By keeping a constant record of the amount of charge 

CHARGE 

STORAGE BATTERY REPORT 
__Exchange Week Ending__— 190 — 


TYPE OF CELL_NO. OF PLATES_NORMAL CHARGING RATE--—AMPERES 

SUMMARY OF DAILY READINGS 



T Ime 
of * 
Charge 

Mean Rate 
of 

Generator 

Output 

Total 

Generator 

Output 

Estimated 
Plant Out¬ 
put While 
Charging 

Estimated 

Battery 

Charge 

Estimated 

Battery 

Discharge 

Maximum 
Rate of 
Plant 
Output 

Test Cell Readings. Cell No*- 

Specific Gravity 
of Solution 

Voltage 

Start 

Stop 

Amperes 

Amp. Hr*. 

Amp Hrs. 

Amp. Hrs 

Amp. Hrs. 

Amperes 

Before 

Charge 

After 

Charge 

Before 

Charge 

* End of 
Charge 

SUNDAY 













MONDAY 













TUESDAY 













WEDNESDAY 













THURSDAY 













FRIDAY 













SATURDAY 














WEEKLY READINGS OF EACH CELL. Date_190_TIME 


Cell Number 

i 

2 

3 

4 

5 

6 

7 

8 

9 

10 

11 

Specific Gravity Before Charge 












Specific Gravity After Charge 












Voltage Before Charge 












• Voltage at End of Charge 












Height of Solution Above Plates 













TEMPERATURE OF AIR-°F TEMPERATURE OF SOLUTION- <T. 

- -a 

WATER ADDED- DATE-ISO- CELL NUMBERS- 


CELL (NUMBERS) EXAMINED WITH LAMP-i-. 

CELL (NUMBERS) WORKED ON--(STATE NATURE OF WORK) 


REMARKS- 


• Voltage reading, to be taken when cell, ore fully charged and the charging current flowing through at the norma) rate. ; 

CORRECT -WIRE CHIEF 

Fig. 290. 

together with the other details as shown in the different columns, a com¬ 
plete record of the performance of the batteries is always at hand, and 
any slight discrepancies can be noted and remedied. 



























































































BATTERIES 225 

In the column “ Time of Charge,” should be placed the time at which 
the charging current was applied, and stopped. 

In column “Mean Rate of Generator Output,” place number of am¬ 
peres of charging current. 

• In column headed “Total Generator Output,” should be placed the 
total ampere hours, obtained by multiplying the mean rate of gen. out¬ 
put, by the number of hours of “Time of Charge.” 

The “Estimated Current Output While Charging” is the estimated 
amount of current used by an exchange during the time of charge, and 
when a discharge ammeter is in circuit with the storage battery, this can 
be ascertained by observing the highest and lowest readings of the dis¬ 
charge ammeter, and then taking a figure which will represent the mean 
rate. From this, the total output while charging can be estimated by 
multiplying this number by the time the charging machine runs. 

The “Estimated Battery Discharge” is from the time at which the 
charging was stopped on the previous charge, to the time the present 
charge was started. 

“The Estimated Battery Charge” is the total generator output minus 
the output while charging. 

“The Maximum Rate of Plant Output” is the highest reading of the 
discharge ammeter while charging. 

A test cell is selected at the beginning of each week. It is best to 
begin with cell No. 1 and continue in regular rotation, until every cell 
is tested every day during the entire week. Have specific gravity and 
voltage before and after charge noted in columns provided for the pur¬ 
pose, and once a week, take readings of all cells and note specific gravity 
and voltage in the columns provided. The other records, such as tem¬ 
perature of air, temperature of solution, etc., are self-explanatory. 

A discharge sheet as shown in Fig. 291 should be provided with space 
for taking the rate of 24 hours discharge. During this time the regular 
charge and discharge of the batteries should proceed without interrup¬ 
tion. 

A reading is taken of the discharge ammeter every 15 minutes. The 
Total Plant Output is found by adding all the ampere readings together 
and dividing by 4, which gives the total ampere hour discharge. 

“Battery Discharge ” is filled in by taking from the time stopped 
charging on the previous charge, to the time started charging on the day 
the discharge readings are taken. 

The “Mean Rate of Discharge” is found by multiplying the entire 
discharge in ampere hours by 4, and dividing by the total number of 
readings taken of discharge ammeter during the test, which is 96. 

The “Excess Charge” equals the battery charge minus the battery 
discharge to the time the charging current is turned on. 

The “ Total Generator Output,” or “Total Charge Current Output” is 
the charging rate times the number of hours the charging current is 
turned on. 

The “Battery Charge” is the total generator output minus the out¬ 
put while charging. 

The “Plant Output While Charging” is the total of the readings of 
the discharge ammeter while charging. 

The “ Percentage Excess Charge” is the excess charge divided by 
the discharge. 







226 


TELEPHONOLOGY 


The record should be taken beginning at the end of the regular 
charge on the 10th and 25th of each month. 

DISCHARGE 

STORAGE BATTERY REPORT 

--Exchange Date Begun_ 190 —. 

Type of Celi _No. of Plates_ Normal Charging Rate-Amperes 

Discharge Ammeter Readings for 24 Hours 
Readings to be Taken Every 15 Minutes 


TIME 

A.M.OR 

P.M. 

AMPERES 

TIME 

A.M. OR 
P.M. 

AMPERES 

TIME 

A.M OR 
P.M 

AMPERES 

TIME 

A.M.OR 

P.M. 

AMPERES 





















































































































































































































— 




































































1 







TOTALS 




. 1 








Total Plant Output_Amp. Hrs. Total Generator Output_Amp. Hrs. 

Battery Discharge_ Amp. Hrs. Battery Charge___Amp. Hrs. 

♦ f 

Mean Rate of Discharge_Amperes Plant Output While Charging_ Amp. Hrs. 

Excess Charge_amp. Hrs. Percentage Excess Charge_ 

v Generator Stopped_Generator Started_ 

Remarks_____ 


NOTE—This form to be filled in beginning at end of regular charge on the 10th and 25th of each month 


Correct---Wire Chief 

Fig. 291. 

Once a year, starting with the battery fully charged, a complete dis¬ 
charge record should be made, reading the discharge ammeter every 15 
minutes. The battery discharge should be continued until one of the cells 
shows 1-9-10 volts. The charging current should then be immediately 
turned on, and continued until the batteries are fully charged. From 



























































































EATERIES 227 

this yearly peformance of the cells the general condition of the batteries 
can be determined. 

To find the percentage efficiency of the battery: 

Find the percentage of the excess charge in the usual manner, and 
divide it into 100. The result equals the percentage efficiency. 

Before beginning this annual test, it is well to fully charge the bat¬ 
teries to 2-5-10 volts per cell, care always being taken to take the readings 
with the battery current on. Then reduce the charge to 1/2 the normal 
rate, and continue charging until the cells read 2-5-10 volts, or as near 
this as it is possible to bring the cells. 

The readings for the battery voltage must be taken with the current 
actually charging the batteries. At the beginning of reading, the charg¬ 
ing rate should be equal to the normal charge rate plus the amount indi¬ 
cated on the discharge ammeter. 

Starting with cell No. 1, test each cell for voltage and specific gravi¬ 
ty every 15 minutes, and proceed in regular order until the last when cell 
No. 1 will again be the test cell and so on to the end of the test. The 
testing record should be carefully preserved, as it will show the actual 
condition of each cell, and also show the efficiency of the battery as a 
unit. 

Where the discharge test is continued through a period when no one 
is on duty in the exchange, arrangements should be made for constantly 
keeping the record, as it is of the utmost importance that the action of 
the cells should be carefully noted. 

*In a 400-line exchange six miles from its main office in a town where 
there is no day lighting circuit, a pole changer is used to supply ringing 
current. The ordinary closed circuit cell only lasted five or six months, 
and when it did give out it did so at the worse possible time. By using 
a portable storage battery a great deal of dirty battery work has been 
done away with, and better service furnished for both the pole changer 
and for the switchboard transmitters. 

There is no noise in the operators’ sets and no cross-talk. The stor¬ 
age cell is charged every three or four days at the main office of the com¬ 
pany where there is charging current available. A portable type, 40 Am¬ 
pere Hour cell is used, and of course, there are two, one being used while 
the other is being charged. 

The exchange troubleman charges them, and it is found that it costs 
less by this method than to use four-gravity cells for each transmitter 
and an Edison-Lelande cell on the pole-changer. The service is also bet¬ 
ter and more reliable. 

This method should find more extended use in private branch ex¬ 
change work, as portable batteries have now reached such a state of per¬ 
fection and are furnished at such low cost that no objection can be raised 
to their use. The first cost scarcely exceeds the cost of 6 gravity cells 
and one cell for the pole changer, while the saving in space is considera¬ 
ble. 

f The simplp storage cell, or accumulator herewith described, is made 
of either cast or bored lead plates, as suits the maker, and has a capaci¬ 
ty of about ten ampere hours. A large sheet of lead one-eighth inch 
thick is cut into plates four inches by five inches in size, care being taken 
to leave a terminal or lug projecting from the plate, as shown in Fig. 

*American Telephone Journal. j-Ey permission—Scientific American. 







228 


TELEPHONOLOGY 


292. It is always best to have the terminals too long rather than too 
short, for the reason that there are certain gases continually rising from 
the acid in the jar, which in time may eat away the brass bolt that 
clamps the plates together; hence the plates make bad connection. After 
the required number of plates have been cut from the sheet, they are 
ready to be bored. In order to avoid burning or bruising the plates, 
clamp them two at a time between two pieces of thin wood in a vice and 
proceed to bore the holes which should be one-quarter inch in diameter. 
If the holes are counter-sunk on both sides of the plates after boring, 
they will hold more firmly. 

Probably one of the best simple methods of casting plates is that 
given by Percival Marshall, which is explained below: 



-CROSS-SECTION OF MOULD. ~ '—rLASTF.R OF PARIS MOULD. —ASSEMBLED PLATES. 


Fig. 292. Fig. 293. Fig. 294. 

On the smooth flat surface of a slab of plaster of Paris, about six 
inches by eight inches by two inches, or of a sufficient size to allow an 
inch or more margin around the grid, carefully make the lines as shown 
in cut, and with a fine chisel proceed to cut away the plaster around the 
squares, beveling it off to a depth of 1-16th inch. The sectional draw¬ 
ing (Fig. 293) will probably give a better idea of how the plaster and 
grooves should be cut. A pouring hole is made at C, which also forms 
the lug o ? the plate; an air hole at A; and a few grooves at B, or at such 
places as would be convenient for aligning the other half of the mould 
when fixing in position for casting. To complete the mould, an exact 
counterpart of the half already obtained must be made. This can be 
easily accomplished by filling up all the grooves (except those marked 
B) with heated paraffin wax, pressing this into position with the fingers, 
and scraping it off level with the surface of the mould, thereby forming 
a pattern of one half of the grid. When the wax is cool and perfectly 
hard, the whole impression may be removed by inserting a pin at one 
corner. Again the grooves of the mould must be filled with paraffin wax 
and scraped clean and level with the surface. The first impression should 
then be laid on its back on the wax at present in the grooves, and the 
whole mould covered with a thin coat of shellac, care being taken to keep 
































































































BATTERIES 


229 


the wax pattern in position. After building a wall of wood or heavy 
cardboard around the mould to a convenient height, the plaster can be 
poured in. When the plaster becomes hard and dry, the mould may be 
taken apart, all wax removed, the halves wired together, and the casting 
of the plates proceeded with. In casting the plates, pure lead and an 
absolutely clean ladle must be used. Thirteen plates (six positive and 
seven negative) will be needed to make the cell, but it is better to cast 
a few plates over and above the number required, as some of them might 
be defective. 

After the plates have been made they are ready to be pasted. The 
positive plates are placed on a smooth slab and pasted with a stiff mix¬ 
ture of red lead and sulphuric acid (one part acid to two parts water). 
The negative plates are pasted in the same manner except that a stiff 
mixture of litharge with the same proportion of acid and water is used 
instead of red lead. The paste can be pressed into the recesses of the 
plates quicker and better by using a wooden spatular. In order that the 
paste may hold tightly, the plates are carefully pasted on both sides. 
When pasted, the plates should be stood up in a warm place to dry. After 
they have become dry and hard, they should be assembled in such a way 
as to allow one positive plate always to be enclosed between two negative 
plates, and the lugs should be accurately fastened together with long brass 
bolts, as shown in Fig. 294. In order to keep the plates well and evenly 
separated, square lead washers are used for the lugs, and wooden racks, 
well boiled in paraffin, for the plates. 

Rubber-coated wires can either be fastened under or soldered to 
the bolts, after which all connections on the lugs must be throughly 
paraffined. The whole mass must then be immersed in a jar containing 
a mixture of sulphuric acid and water (four parts water to one part acid.) 

Some little care must be exercised in connecting up the cell, to make 
sure that its positive pole is joined to the positive pole of the source of 
supply, and, as the E. M. F. of the primary battery or the dynamo is in 
constant opposition to that of the accumulator, it is necessary that this 
E. M. F. exceed that of the latter in order that the current shall flow. 

An easy way to determine which is the positive pole, if the source 
of current is from an electric light circuit or a dynamo, is to hold the 
two wires in a glass of water, as previously described, or testing paper 
may also be made by immersing strips of white blotting paper in a thin 
solution of white starch, and, after drying again dipping them for a few 
seconds in a solution of one-half ounce of potassium iodidq in one pint 
of water. A piece of this paper, moistened and having the two wires 
applied to it half an inch apart, will turn red at the negative pole and vio¬ 
let at the positive. 

The time taken to charge a storage cell depends entirely upon its 
capacity. For instance, if the cell has a capacity of 10-ampere hours, 
and the charging current is two amperes, the time taken for charging 
equals 10 divided by 2, which is 5 hours. The formation of the plates 
in the first place takes a much longer time—anywhere from 25 to 50 
hours, with this amount of current. When the plates are fully formed, 
the positive will be dark chocolate color, and the negatives a dark slate 
color. The cell will boil and gas freely, and the voltage will reach 2 y 2 
while the charging current is on. These latter conditions always occur 
with a fully charged cell. By all means never short circuit, i. e., spark or 
flash the terminals of a storage battery together to see if it is charged; 





230 


TELE PHONOLOGY 


this is very detrimental, and will in most cases ruin any accumulator. 
A very handy way of roughly telling whether a battery is fully charged, 
or run down, is to connect a two-volt lamp across any single cell to be 
tested. If the lamp glows brilliantly, the cell is fully charged, but if it 
gives a dim light, the cell is discharged. When the voltage reaches 1.7 
under discharge, the cell is empty and should be recharged at once. A 
small pocket voltmeter is best for testing the amount of charge in the 
cell. The voltage should be taken while the cell is discharging. 

The E. M. F. of a lead storage cell is 2 volts, and its amperage 
(capacity) varies in proportion to its size. Each square foot of positive 
surface gives about 6 ampere hours; therefore, if you have a battery of 
four inches by five inches in size and containing thirteen plates (six posi¬ 
tive and seven negative), the ampere would equal: 

4 in. x 5 in. x 2 sides x 6 plates 


44 sq. ins. 


x 6 amp. hrs. = 10 amp. hrs. 


If it is desired to charge any number of storage cells connected in 
series, i. e., the positive pole of the first joined to the negative pole of the 
second, etc., multiply the number of cells by 2 1 / 2 , which will give the 
voltage of the charging current required. 

Storage batteries are usually installed with a sufficient number of 
plates to furnish current for the present needs of the exchange, but the 
jars or tanks are made of sufficient size so that additional plates may be 
installed as the exchange increases in size. For this reason when the 
battery is installed care should be taken to secure jars large enough to 
permit of the addition of enough plates to give a current output to operate 
the ultimate number of subscribers the switchboard will accommodate, for 
at least 36 hours. 

1 

It is customary to install two sets of batteries, and to provide dupli¬ 
cate means of charging same, so that one set may be charged while the 
other is being discharged. While this undoubtedly is the safest plan, as 
a reserve battery is always at hand, still with modern equipment and 
methods of charging the additional expense would seem unnecessary as a 
properly maintained battery seldom becomes inoperative and modern 
methods of charging and sources of current supply are very reliable. 
After the exchange has outgrown the initial capacity of the battery and 
it becomes necessary to add more plates, with some makes of battery it 
is advisable to re-arrange the old plates so as to form complete cells with 
them, and use the new plates to form complete cells. New and old plates 
do not always work well when placed in the same cell owing to a differ¬ 
ence in the capacity of the plates, the old ones being undercharged when 
the new one would be fully or over charged. 

In the majority of common battery systems it is customary to ground 
one pole of the battery. This is done to secure the operation of trunk 
signals between different exchanges and for the purpose of preventing 
electrolytic action, which is a form of decomposition or corrosion which 
results at joints and terminals when the current flows from the + pole 
to the — pole. If the lines should be -(- and the — pole of the battery be¬ 
comes grounded, this action would sometimes result, so it is obviated by 
permanently grounding the + pole of the battery, therefore the leak, if 
any, from the lines, is always in the opposite direction from that which 



BATTERIES 231 

would tend to produce a corrosive action, as this action is present at the 
-f pole only. 

The resistance of the leads or main wires between the storage bat¬ 
tery and the power board where the battery is connected the various 
switchboard circuits should be very low, as any resistance in this circuit 
will cause cross talk. 

This resistance in repeating coil systems should not exceed .07 ohm, 
including the resistance of the batteries which is but a fraction of this. 

In retardation coil systems much higher resistance leads can be 
used, but in either case the resistance should be kept as low as possible. 

The current carrying capacity of the leads should at all times greatly 
exceed the maximum amperage that the switchboard will ever require. 
If the resistance is kept within the limits above given, it will be found 
that in most cases except where the battery is very near the switchboard 
apparatus, ample carrying capacity will be obtained. 

The methods o'’ computing the battery capacity for a switchboard 
depend upon the type of equipment, etc. The traffic conditions of course 
directly determine how much work the battery must do, so before the 
exchange is installed a careful study must be made to determine the 
greatest load, duration of same, and the other details. This data must be 
given the switchboard manufacturer who can then easily determine the 
battery capacity necessary. 

The capacity of a storage battery is usually rated in ampere hours, 
that is a 40 ampere hour battery would deliver 1 ampere for 40 hours, or 
2 amperes for 20 hours, etc. Batteries are usually rated by the manufac¬ 
turers as having a certain discharge for 8 hours, 5 and 3 hours, never 
exceed the discharge limits as given. It will be found in most cases that 
the charge rate is the same as the 8 hour discharge rate, that is if the 
8 hour discharge rate is 3 amperes per hour the normal charging rate 
will be 3 amperes. The nearer a battery is operated within the normal 
charge and discharge rate, the better condition it will remain in. When 
the battery is not discharged enough it suffers almost as much as if it 
is under or over charged. 

The method of charging from a direct lighting circuit, as outlined 
in the first part of this chapter, is exceedingly wasteful and only practi¬ 
cal when a cheap source of current supply is available and a battery of 
small capacity is used. 

A very successful method of charging is by means of a motor-gener¬ 
ator, the motor being driven by a direct or alternating current of from 
100 to 500 volts, and being belted or direct connected to a generator of 
proper voltage and amperage to charge the battery. The output of the 
generator must always be 2.5 X the number of cells in the battery. The 
amperage must be the charging rate of the cells, plus the discharge o 
the cells at the time they are being charged if they are charged while 
in service. As an illustration: A dynamo for charging a battery of 11 
cells, whose charging rate is 3 amperes, and which are discharged at the 
rate of 1 ampere, would have a voltage of about 30, (11 X 2.5 = 27.5 = 
voltage of battery at full charge) and an output of at least 4 amperes, 
(3 amp. normal chg. rate + 1 amp. disc.) A regulating resistance is 
usually inserted in the circuit so that the charging current can be varied 
at will. 








232 


TELEPHONOLOGY 


A very satisfactory method of charging is to use a gas or oil engine, 
connected to the dynamo. This method is desirable where there is no 
available current supply for driving a motor, or where the cost of cur¬ 
rent to run the motor would be excessive. Care must be taken when 
securing this outfit to have a special engine, or equip the dynamo with 
a fly wheel and use a loose belt, so that a uniform speed will be obtained, 
as an irregular running dynamo may cause noise in the talking circuits. 
In all cases the charging dynamo should be especially adapted to this 
work. It should have a large commutator with many segments so that 
a smooth uniform current will be produced. 



Western Electric Co.’s Charging Generator. 


The Mercury Arc Rectifier is peculiarly adapted for charging the 
storage batteries commonly used in telephone exchanges, where only an 
alternating current service is available. It creates no disturbance on 
the telephone circuits. The efficiency is high, the first cost and main¬ 
tenance low, and in addition only a small floor space is occupied. The 
General Electric Company has recently placed on the market a complete 
line of sizes up to 50 ampere capacity, especially adapted to meet the re¬ 
quirements of telephone exchanges. 

The rectifiers are constructed to give any D. C. voltage required by 
the batteries. When charging 17 cells, as is commonly done in telephone 
practice, the rectifier will have an average efficiency considerably greater 
than a motor generator set o p the same capacity. This efficiency is in 
the neighborhood of 60% and is maintained at partial as well as at full 
load. If the direct current is delivered at a higher voltage, viz.: when 
more cells are charged in series, the efficiency will be correspondingly 
higher. Hence, where possible, it is advantageous to charge two or more 
batteries in series. This rise of efficiency with the voltage is due to the 
fact that the voltage drop in the rectifier tube is constant, and therefore 
the percentage loss is less, the higher the voltage. 

The essential properties of mercury vapor as utilized in the rectifier, 
and the action of the tube is simple, and may be described as follows: 

In an exhausted tube provided with a mercury cathode and one or 
more anodes, mercury vapor in the ionized state is supplied from the 



BATTERIES 


233 


cathode, when the latter is in the state of excitation. This excitation is 
maintained only as long as current flows between the cathode and one 
or other of the anodes. With the ionized vapor present in the rectifier 
tube, current can flow only as long as the mercury terminal is negative. 
If, the polarity of the voltage is reversed so that the mercury electrode 
becomes positive, the excitation, and therefore the flow of current ceases. 
The two anodes of the rectifier are connected to the A. C. source, and the 
cathode through the load to the neutral point between the two anodes. 
Therefore, with the cathode excited, current will flow alternately between 
the cathode and each anode in turn, the cathode always being negative. 
Unless some means is provided to maintain the arc over the zero point 
of the wave, the cathode will lose its excitation, and the tube will not be 
continuously operative. In order to maintain the arc, the current from 
the line, after passing through the arc and load, returns to the other side 
of the line, through a reactance. This reactance is charged during the 
greater part of each wave, and discharges through the zero point, thus 
maintaining the arc until the other anode has become positive, when the 
action is repeated with the second half of the rectifier active. Hence, 
there is a continuous flow of current in the same direction at the cathode 
and through the battery, although in other pars of the circuits, the polar¬ 
ity changes. The reactances, in discharging during the zero point of the 
wave, reduce the fluctations in the rectified current. Thus, a true contin¬ 
uous current is produced with only a small loss in transformation. 



Fig. 296 


Fig. 295 


The tube is started by a slight rocking motion, which bridges the 
mercury between the cathode and an additional starting anode, connected 
through resistance to one of the A. C. lines. When the tube is returned 
to a vertical position the mercury bridge breaks, and a small mercury 
































234 


TELEPHONOLOGY 


vapor arc is started which furnishes the initial cathode excitation and 
enables the current to pass between the cathode and working anode. 

The magnitude of the current pulsations depends on the amount 
of reactance in the circuit. Since in telephone work, an extremely smooth 
current is required, more reactance is used than is common when the rec¬ 
tifier is employed for other purposes. 

Fig. 295 shows one type of rectifier panel used for telephone instal¬ 
lations. The panels can be readily operated in parallel with one another 
or in parallel with other direct current sources, such as engine driven 
generators or motor generator sets. Fig. 296 shows the circuits of the 
complete outfit. 

An occasional renewal of the tube is the only operating expense aside 
from the current required. 



Fig. 296a. 


Fig. 296b. 


Fig. 296c. 


Another type of rectifier consists of a solution in which is immersed 
one lead and one aluminum electrode. The alternating current is caused 
to flow in series through the battery and the two rods. This arrangement, 
which is termed a chemical rectifier, possesses the peculiar property of 
allowing the current to pass only in one direction, and therefore the alter¬ 
nating current is changed to a direct current pulsating in character. 

The aluminum rod is always positive ( + •) 

This device may be connected directly to an alternating current, a 
regulating resistance being placed in series with the battery to regulate 
the current. When this is done considerable energy is wasted, it is there¬ 
fore customary to use a transformer, and step down the alternating cur¬ 
rent to about the voltage of the battery, and then pass it through the rec¬ 
tifier. A choke coil may be used for this purpose but is not so efficient. 

Fig. 296a shows the connections of a chemical rectifier when connect¬ 
ed directly to the A. C. Mains. To protect the rectifier and limit the 
amount of current flow, lamps are placed in circuit as shown. 

Ordinary 6x8 battery jars may be used. The solution being 21^ lb. 
each, sal ammoniac and common salt, dissolved in 6 gal. water. The alum¬ 
inum (-f) electrode is a rod % in diameter and long enough to reach 5 in. 
into the solution. The lead (—) electrode is a 1 in. square rod, or sheet 
of lead 14 in. thick by 2 in. wide. 

As this arrangement only utilizes one half the cycles, it is not effi¬ 
cient, and the method shown in Fig. 296b is recommended. 














































































BATTERIES 


235 


Here four jars are used, arranged as shown. Sufficient lamps are used 
to limit the current flow. 

A more economical arrangement is shown in Fig. 296c. A trans¬ 
former is used, which steps the A. C. current down to about the desired 
voltage. One lead and two aluminum electrodes are used. With this ar¬ 
rangement a very smooth current is obtained, suitable for charging tele¬ 
phone batteries in exchanges using the impedance coil type of circuits. 
When repeating coil cord circuits are used, this method is liable to pro¬ 
duce noise. 

Fig. 296c shows an ammeter and reheostat connected in circuit, the 
former for measuring the charging current, and the latter for measuring 
the current flow. 

Care should be taken not to heat the transformer, or to let the recti¬ 
fier solution become too warm. The latter can be obviated by using a 
large vessel to hold the solution, and making the electrodes somewhat 
larger. 

With all types of charging equipment using alternating current, 
some arrangement is necessary to prevent a noise in the battery caused 
by the uneven current pulsations. These devices consists of coils, or 
condensers are bridged across the charging mains. When properly 
designed and installed rectifying devices may be used to charge the battery 
at the same time it is connected to the switchboard, without any inter¬ 
ference in the talking circuits. 

The necessary switches, instruments and other equipment for test¬ 
ing the charging current, and the lay out of the fuses for the different 
circuits jrom the battery to the switchboard apparatus are described 
elsewhere. The various arrangements are as numerous as types of 
switchboards themselves, each installation often being arranged to meet 
certain special conditions. 

The internal resistance of storage batteries is very low, and should 
form only a small part of the entire resistance in which they are placed. 

Other batteries, especially dry cells often increase enormously in 
resistance as they become exhausted and it is often necessary to know this 
resistance, when making calculations as to the total resistance of the 
circuit. 

The internal resistance of a battery may be determined by means of 
a voltmeter and resistance box, arranged as shown in Fig. 297. Proceed 
as follows: 

Take voltage of D with key open; this will be called D. Then depress 
key, and take voltage which is D, Then the resistance X of the cell is: 

D — D, 

X = r X - 

• D, 

r = Resistance of coil used. This may be varied to obtain the best 
results. 

The resistance may be measured with an ordinary Bridge by arrang¬ 
ing the connections as shown in Fig. 297a. The resistance X of C is 

A 

R — = X 
B 



236 


TELEPHONOLOGY 


R = resistance of variable arm, A, one arm of bridge, and B the 
other arm. The battery is connected to the X posts. 

Another method is to use the slide wire bridge which may be con¬ 
structed from a yard of German silver or copper wire of nearly any 
guage. This wire is stretched across the scale, as shown in Fig. 298. A 
known resistance must be used. Connect battery as shown. A re¬ 
ceiver is used in place of the galvanometer, a generator being used for the 
testing current. Slide contact C along the wire until a point is reached 
where no sound is heard; then the number of scale divisions on the B slide 
of the scale, divided by those on the A side, multiplied by the resistance of 
Ri will give the resistance of the battery. 



Suppose the scale has 1,000 divisions and a balance is found 400 
divisions from A. The total length of the scale is 1,000 divisions, and the 
coil R x is 1 ohm. Then the number of divisions from C to B, divided by 
the number of divisions from C to A and this multiplied by the resistance 
of R, will give resistance of battery. F°r instance, in the example just 
given: 


C to B + 600! C to A = 400. 600 -r- 400 = 1.5. -f- 1 (res. of RJ 
— 1.5 ohm, res. of bat. 


The contact is moved along the wire until no sound is heard in the 
receiver, then the resistance of the cell is determined the same as for 
method shown in Fig. 297. 

Fig. 299 shows another method, using an ammeter and voltmeter. 
First measure the voltage without pressing key K. Call this V. Then 
press key, putting circuit through ammeter A and resistance R, call the 
voltmeter reading V 1 and the armeter reading A. Then the resistance of 
the battery X is: 


V 



X 


A 




























I 


CHAPTER VIII. 


TESTING TELEPHONE PARTS. 


Transmitter Testing .—There are two classes of tests which are ap¬ 
plied to transmitters, a, routine or factory tests, and 6, special or research . 
tests. The first class is used in testing the finished product of a factory 
to make sure that no defective goods are shipped. It is necessarily a 
rapid test and omits many of the features which would come in if new 
facts were to be discovered instead of merely passing on the standard 
qualities of a large number of transmitters. Special or research tests 
are of so varied a nature that no one description can cover them all. The 
latter are confined to the laboratories of universities and those manufac¬ 
turing companies who are striving to better their product. 



Fig. 300. 


Fig. 301. 



Essentially the routine test of a transmitter consists in inserting it 
into a circuit like the one in which it is designed to operate, ^he other 
parts of the circuit are made up of parts of apparatus which are of known 

excellence. 

Figure 300 shows the simplified circuit as used to test local bat ^Y 
transmitters. Std. is the stand ard transmitter, and L is jthe_one_which 

*This Chapter, with the exception of the matter describing standards of Sell Induc¬ 
tion at end, written by Arthur Bessey Smith, Professor of Telephone Engineering, 

Purdue University. 


237 
























































238 


TELEPHONOLOGY 


is under test. There is yet no mathematical or other exact test to apply 
to a transmitter to aid a person in selecting his standard. Out of a large 
number a careful selection is made by testing the transmitters one against 
the other, in each case retaining the better one of the two. The ear of 
a trained observer is the standard. By continually turning his attention 
to the qualities of all the transmiters he uses, he may become quite expert 
in detecting those qualities which are not desirable as well as those which 
go to make up loud and distinct transmission. It is not very hard to make 
a transmitter which possesses either of these qualities alone, but to be 
' loud without losing in clearness is a very great art. 

It will be noted in the figure that the two transmitters are placed in 
series with a 4-volt battery, the primary winding of a local battery induc¬ 
tion coil, and a milliammeter. The receiver is on a closed circuit with 
the secondary. The standard and the unknown are in series with each 
other, but one of them is normally shunted by a switch. By operating 
this switch, the tester can instantly change from one to the other and 
thus compare them with the most accuracy. It is a noted fact that the 
eye ard ear are very poor in remembering the intensity of the phe¬ 
nomena with which they deal. You can not look at a light on one even¬ 
ing and compare its brilliancy with that of another which you can see 
on the next night. Yet if you had them side by side you might notice 
quite a difference. It is even so with sound. The change from one trans¬ 
mitter to the other must be quick, in order that the ear may not forget 
the loudness and quality. A low reading voltmeter is conected across 
the transmitter so that its behavior with regard to resistance can be 
determined. This is one of the valuable aids to the tester in showing 
up defective assembly and poor carbon. The voltage shown by the volt¬ 
meter divided by the current given by the milliammeter gives the resist¬ 
ance, according to Ohm’s law. From experience with the regular run 
of transmitters which the factory is putting out, the tester knows about 
what the resistance of a good one should be. When a new transmitter 
has been put in place for test, and the battery circuit closed, the current 
should rise more or less rapidly, then slow down and stop, fall a little, 
then rise till it reaches a more or less steady condition. In crome cases, 
the falling back in current may be very slight, only amounting to a sta¬ 
tionary position of the needle. But in good transmitters, this peculiar 
action is rarely missing. After allowing the current to become steady, 
the tester will talk into it. This should immediately produce a lowering 
of the current, as when the carbon granules are agitated, they press more 
loosely on each other and so have a greater resistance. 

In Figure 301 is shown the simplified arrangement for testing com¬ 
mon battery transmitters. The battery, now 24 volts, feeds to the cir¬ 
cuit through two retardation coils having 50 ohms resistance each. The 
receiver is bridged across the circuit with a condenser in series to keep 
battery current out of it. Each transmitter in turn is placed across the 
line with only the milliammeter in series. The battery current is kept 
in the main circuit consisting of battery, retardation coils, milliammeter, 
and transmitter. The undultations caused by the transmitter act as an 
alternating current in the circuit composed of the transmitter, milliamme¬ 
ter, receiver, and condenser. This is similar to the conditions of a short 
line. By throwing the key, K 4 , an additional resistance may be inserted 
to imitate the condition of a long line. The exact resistance of this coil 
depends on the severity of the test desired, and may vary with different 
manufacturers. The resistance of the retardation coils and the voltage 


TESTING TELEPHONE PARTS 


239 


of the battery also depend on the system, as, for instance, a manufac¬ 
turer who uses 40 volts on his switchboard, would doubtless use the same 
on his testing circuit, with retardation coils to suit. The gen¬ 
eral features of the test are the same as in local battery work, except 
that the resistance of the transmitter will be higher. Local battery 
transmitters run from 20 to 35 ohms, while for common battery it is from 
50 to 100 ohms. Some people state the resistance of the transmitter at 
rest. Both the resistance at rest and in motion should be given, though 
the latter is dependent to some extent on the loudness of the sound which 
is causing its agitation. 



Fig. 302. 

Fig. 302 shows how the two circuits of Fig. 300 and 301 are combined 
into one, with all necessary switching facilities. There are seven keys 
each operating from one to four springs. The battery is in two groups, 4 
and 20 volts each, making a total of 24 volts. In the normal position ol 
all the keys, the battery is on open circuit. Key No. 1 controls the 24 volt 
battery, 'it consists of two main springs, each marked No. 1 in the draw¬ 
ing, and operated simultaneously by the same cam. Key No. 2 contros 
both the main circuit to the transmitters and the plus end of the volt¬ 
meter. If we throw keys No. 1 and 2, we get the circuit connection for 
common battery testing, the same as was shown in Fig. 301. By operating 
key No. 7, the tester can cut the unknown transmitter out and the stand¬ 
ard in. 

Releasing both keys puts the circuit again in the position of rest. 

Key No. 3 controls the change to local battery testing. It consists ot 
four main springs which are operated at the same time by one cam or 
lever. They are all marked No. 3 in the figure. The two upper mam 























































240 


TELEPHONOLOGY 


springs- do the switching from 4 volts to 24 volts. The lower left spring 
switches the transmitters, while the lower right spring attends to the 
voltmeter. Thus with one motion, all the necessary changes are made for 
changing from common battery to local battery, except switching the re¬ 
ceiver and putting in a local battery standard transmitter in the place of 
the common battery standard. The last operation is easily done as each 
of the three transmitters is held in a specially designed shell, with spring 
contacts. 

The actual arrangement of keys is shown in Fig. 303. As the keys 
are all numbered the same in all the figures, further explanation will be 
unnecessary, except to give a summary of their grouping. 



For common battery, throw keys No. 1 and 2, leaving all others nor¬ 
mal. Operate No. 7 to cut in either the standard or the unknown. Throw 
No. 4 for line effect. 

For local battery, throw keys No. 2, 3, and 5, leaving all others normal. 
Operate No. 7 to cut in either the standard or the unknown. 

Testing the Resistance of Transmitters —There are two means 
which are used for the measurement of transmitter resistance, the 
Wheatstone bridge and the voltmeter-ammeter method. Of the two, the 
latter is without doubt the more satisfactory. Any steady resistance of 
reasonable magnitude can be most accurately measured by the bridge, 
provided the unknown resistance does not contain any electromotive 
force. The transmitter is on the border line, being sometimes steady and 
sometimes exceedingly variable. If we take a transmitter which' has 
been out in service for some time, have the room quiet, and measure its 
resistance thus, we can get very good results with the Wheatstone bridge. 
The resistance will be rather low, perhaps 10 to 20 ohms in the case of 
a local battery transmitter. If we now shake it and immediately measure 
again, we shall find that the resistance has risen and is quite variable, so 













































































































TESTING TELEPHONE PARTS 


241 


that it is not easy to get a reliable result with the bridge. This is because 
the particles which be'ore were more or less packed together by the set¬ 
tling action of time and use, are now in a very loose condition and the 
slightest jar causes them to slide on one another, thus changing the re¬ 
sistance. Since the measurement with the bridge depends on carefully 
adjusting a resistance, usually with plugs, it takes time. During this the 
resistance of the transmitter may change very materially. So for all but 
a very small class of measurements the bridge is not suitable. 

In the use of the second plan, a milliammeter is placed in series with 
the transmitter and a voltmeter shunted around the latter. The former 
instrument should have a range of from zero to .150 amp. or perhaps 1.00 
amp. It should be a good, sensitive instrument, having a very small re¬ 
sistance and negligible inductance. The resistance can be measured on 
a Wheatstone bridge, taking care that the measuring current goes 
through it in the direction which will deflect the needle positively and not 
stronger than the ammeter will stand. A Weston milliammeter with a 
scale 0-150 milliamperes will have a resistance approximating .3 ohm. 
The inductance can be best tested by inserting the milliammeter in the 
primary circuit of a local battery telephone and connecting the telephone 
to a receiver in another room. Talk to an observer at the distant receiv¬ 
er, meanwhile short circuiting the ammeter and removing the short at ir¬ 
regular intervals. If the impedance is low enough to be negligible, the 
observer will not be able to tell when the short is on or off*. ,^.-*1 

The voltmeter should be an efficient one, wth a scale not very much 
in excess of that which will be applied to the transmitter. For local bat¬ 
tery work 5 volts is a good figure, since 4 volts is what should be applied. 
For common batttry transmitters it may take a 15 volt scale. Be sure 
that your voltmeter has a high resistance. It should be at least 50 ohms 
per volt of scale. This makes the 5-volt scale require 250 ohms. lOOHo 
130 ohms per volt will be better, making the voltmeter from 500 to 650 
ohms. If the resistance of the voltmeter is too low, it will make an error 
in the current reading, wMch will consist of the current {Stken by the 
transmitter plus that taken by the voltmeter. The correction is as fol¬ 
lows : 

Let I = current reading as per milliammeter. 

I () = true value of current through transmitter, 
e = voltage across transmitter, shown by voltmeter. 

R v = resistance of voltmeter. 

Then the true current through the transmitter will be 

e 


R v 

If the resistance 0 " the voltmeter is high, this correction may be neg¬ 
ligible. For instance, there are some voltmeters on the market with a re¬ 
sistance as low as 20 ohms per volt. Suppose that we have a common 
battery transmitter to test and the scale of the voltmeter is 0-15. This 
makes its resistance 300 ohms. Suppose we take the following readings, 
voltage, 5; current, .1167 amp. If we take no account of the correction, 
we arrive at the transmitter resistance by dividing the voltage by the cur- 
16 







242 


TELEPHONOLOGY 


rent, giving 42.9 ohms. If we get the true resistance by correcting for 
the current taken by the transmitter, we shall have the following: 

Voltmeter current, .0167 amp. Transmitter current = .1167 — 
.0167 = .1000 amp. True resistance, 50 ohms. If a better voltmeter 
had been used, having 100 ohms per volt, the calculated resistance would 
have been 49.8 ohms, which is so near the truth as to make closer work 
unnecessary. 

It may be well at this point to consider in detail the features of 
transmitter resistance. When at rest, the resistance is of some value. 
Call it R. At first thought one would suppose that when waves of air 
carrying the voice strike the diaphragm, they would cause a simple, vary¬ 
ing pressure on the carbon. That is, the initial pressure would be in¬ 
creased and decreased by a certain value. The crest of the wave in air is 
the point of maximum pressure, so that it presses hard against the dia¬ 
phragm. The trough of the wave in air is the point of minimum pres¬ 
sure, so that there is a partial rarification or vacuum in front of the 
diaphragm. This draws the diaphragm out and makes the pressure on 
the carbon particles less than it was when at rest. This makes the re¬ 
sistance greater than normal. Let r be the small resistance which is ad¬ 
ded to the resistance of rest during one portion of the wave, and sub¬ 
tracted from it during the other. In a certain way this is what does nap- 
pen in action. According to this, it would be just as accurate to measure 
the transmitter resistance with the diaphragm at rest as in motion, for 
the average resistance would be the same as the steady resistance when 
at rest. However, when we experiment by taking the resistance of any 
transmitter while agitated by a steady noise, we find that the average re¬ 
sistance as shown by the voltmeter and milliammeter is higher than when 
at rest. From this fact we reason that during operation the particles of 
carbon are kept in motion by the diaphragm and never settle down. Thus 
the pressure between them is less and the resistance consequently higher. 
We now review our statement and say that R= average or steady resis¬ 
tance of transmitter while operating, r == small resistance which is ad¬ 
ded to or subtracted from the average resistance, caused by the changes 
in pressure. 

Of course, the value of r changes from moment to moment with the 
irregularities of the voice, and is only introduced here to aid in getting an 
idea of the operation of the transmitter. 

The resistance of the transmitter as measured by the means above 
described consists of several parts. 

a. Resistance of wires in the transmitter and all conducting parts, 
up to the surfaces of the electrodes. 

b. Steady portion of carbon resistance, that which never changes. 
This does not mean the resistance of the carbon in the carbon electrodes, 
but the resistance of the carbon in the granules and that portion of the 
contact resistance between the granules which does not change. 

c. The variable contact resistance, which changes from zero to a 
maximum and back again to zero. It is this portion which does the 
talking. 

The above analysis of the portions of resistance in the transmitter 
are better shown by Fig. 304. While operating, the resistance at any in¬ 
stant is composed of three parts, a, b, and c. The last part, c, is the only 
part which has anything to do with varying the current and so transmit¬ 
ting speech. The figure is not intended to represent any particular sound, 


TESTING TELEPHONE PARTS 


243 


being any curve in general. The broken line R through the portion, c, in¬ 
dicates the value of the average resistance. The distance vertically from 
the base line to the line, R, is the average value as shown by the volt¬ 
meter test. It is not necessarily true that the resistance varies as much 
above this line as below it. There are very good reasons for believing 
that for any steady, musical note, the deviation from the average line up¬ 
ward is greater than the deviation downward. One reason for this belief 
is that the pressure-resistance curve for carbon is in form similar to a 
hyperbola. The other is that such a curve is necessary, if the current in 
the primary circuit is to be an exact duplicate of the sound wave in air. 

The best way to obtain a steady sound for transmitter testing is 

doubtless the use of a receiver in front of the mouthpiece. Pass a steady 

alternating current though the receiver, taking it from 60 cycle lighting 
circuit if no other is available. 2000 or 3000 ohms may be inserted in 

series to regulate the flow of current if the voltage is 110. The exact 

value of this resistance will depend on how loud a noise is desired. In 
order that the best effect may be secured, the receiver must be as close as 
possible to the transmitter, touching the mouthpiece. If a long series of 
tests are to be made with the same transmitter, it is best to lash the re¬ 
ceiver to the mouthpiece with a few layers of tape. This will close all 
openings and confine the sound from the receiver, making all of it act on 
the diaphragm of the transmitter. But if many transmitters are to be 
tested in succession, merely holding the receiver to the mouthpiece will 
give excellent results. 




■< ---► Time. 

war#- Le h gtK 


The selection and test of the granular carbon used, is highly impor¬ 
tant. One method of manufacturing the granules is as follows: 

Select very pure, hard anthracite coal from which to make the car¬ 
bon. Cross Creek Lehigh coal is said to be the best, and if trying a new 
kind, have it analyzed for foreign substances. Look out for slate and 
anything else, as you want pure carbon. Select clean, shiny, crystalline 
pieces showing no stratification, no dull appearance of slate, dirt, or 
other impurities. 

Break to size of walnut and inspect again. Finally crush to nearly 
desired size. Put into graphite crucible and cement the cover on with 
fire clay. The cover must have a hole in it about half an inch in diametei. 
Leave this hole open during the first part of the firing till the bulk of the 
volatile gases has passed off. This is where experience is the only guide, 
both as to tempeprature and time. Then plug up the hole and raise the 
temperature to white heat and hold it there for about 12 houis. The car¬ 
bonizing must be thorough, for if not, the resistance will be abnormally 
high. 


































244 


TELEPHONOLOGY 


Let it cool very slowly till cold enough to handle with the hands. Un¬ 
seal the small hole in cover and pour the granular carbon out. It is not 
necesssary to remove the cover at each firing, for a new lot of granulated 
coal can be introduced through the small hole. Screen the completed 
product through two screens. For local battery transmitters, use a No. 
60 mesh (60 meshes per inch) and reject all the larger granules which 
are caught by the screen. Take that which passes through the screen 
and screen again with No. 65 mesh, rejecting all that passes through. For 
common battery transmitters screen similarly, but use No. 100 and No. 
110 mesh. 

A very good way to test the carbon is to put a regular charge of it 
into a transmitter capsule, electrodes vertical as in use, and pass about 
one tenth of an ampere battery current through it. Measure current 
with milliammeter and voltage across the capsule with low reading volt¬ 
meter. The main requisite is that the granular carbon shall not change 
with time. At first there will be some fluctuations till conditions get 
steady, but if the carbon is good it will settle down to a steady resistance. 
Fig. 304a shows a local battery arrangement. The cell should stand 4 
volts ard not hiss, the latter tested by the receiver. Fig. 304b is for com 
mon battery granular carbon and should not hiss on one tenth ampere. 



Testing of Transmission —Transmission, as used by telephone engi¬ 
neers, is a term applied to the total operation of transmitting the voice 
from one point to another. It is in many respects similar to transmission 
as used by power engineers, in that we have an amount of energy in-put 
at the sending end of the line, and a smaller amount of energy out-put at 
the receiving end. The ratio of the energy delivered to the energy put in 
at the sending end constitutes the transmission efficiency. It is the object 
of good engineering to make this ratio as high as possible. But in the 
telephone we have an added object of which we must not lose sight. Not 
only must the sound at the receiving station be as loud as possible, but it 
must have as nearly as possible the same wave form as the original wave 
which enters the sending apparatus. This is the same as saying that the 
conversation must be clear. The words which are spoken into the trans¬ 
mitter consist of air waves. An air wave consists of a condensation and 
a rarification. The former means that the air is compressed slightly 
more than the normal air pressure as shown by the barometer. The lat¬ 
ter means that the air has a slightly less pressure than the normal air 






































TESTING TELEPHONE PARTS 


245 


pressure. A continuous sound means a continuous procession of conden¬ 
sations and rarifications, one after the other, moving at the speed of 
sound, which is about 1000 feet per second. If we could “freeze” these 
sound waves into air and measure the pressure at a number of points in 
a straight line, \ye could plot a diagram or picture of the wave. We might 
let a horizontal line represent time and mark off on it from a fixed point 
the length of time taken for the air wave to pass from one condensation 
to the next. We can do this by saying that we will let each inch represent 
1/100 second. If the sound has about the pitch of one octave below mid¬ 
dle C, there will be not far from 125 waves in a second. Then the length 
of the wave will be .008 of a second, which when plotted on our scale (one 
inch = 1/100 second) will equal .8 inch. If we erect at the various 
points along this wave length lines which represent by their length the 
presssure of air at the different instants in the wave, a line drawn 
through the tops of these vertical lines will show us the form of the air 
wave. Fig. 305 gives an idea how this may be done. The broken line, P, 
represents the normal pressure of the air as shown by the barometer. 
The condensations and rarifications are deviations from this average 
pressure. 

If the sound is a pure, simple musical note, the shape of the wave in 
air is a sine wave. That is, if the length of a wave be considered 360 de¬ 
grees, the length of any perpendicular from the broken line, P, to the curve 
will be proportional to the sine of the angle represented by the number of 
degrees from zero to the foot of the perpendicular. There are very few 
purely sinusoidal waves in air, although there are some which closely ap¬ 
proximate it. Most sounds have a fundamental or prevailing note with 
other waves mixed up with it. This is especially true of the voice. When 
speaking, the fundamental is the general tone of the voice. With men it 
is lower than with women and children. The voice of a man runs some¬ 
where between 100 and 200 cycles per second, while women’s voices come 
about 300 to 400. It is very difficult to fix the limits, as it varies with dif¬ 
ferent individuals. It also varies in the same person, as when a man 
raises his voice in calling, or in an excited debate, or lowers it in a con¬ 
fidential talk. The fundamental is the controlling frequency, but super¬ 
imposed on it are multitude of higher frequencies which are essential to 
the voice. These higher frequencies are called “upper tones” or “higher 
harmonics.” They are some multiple of the frequency of the fundamen¬ 
tal. If we could suppress all the upper tones, we could not tell what a 
man was saying. All voices would sound alike. It is by the skillful com¬ 
bination of upper tones that the organs of speech form words. There¬ 
fore it is necessary that any device for transmitting speech to a distance 
shall transmit all the frequencies with equal force. Further, it must not 
change the phase relationship between the various frequencies. If in 
transmission the fundamental loses half its original force, speech will 
still be clear i all the upper tones also lose half their forces. But if some 
of the frequencies are suppressed much more than others, speech will 
tend to be thick, confused, and hard to understand. It may be very loud, 
but if the relations between the fundamental and the upper tones are 
much disturbed it will be hard to understand. It is sometimes better to 
have the sound weak and clear, than loud and confused. Just how much 
suppression a given note can suffer without being noticed by the ear is 
not known. The amount o" phase displacement which will not affect 
speech is also unknown. It undoubtedly differs with individuals, for 
some people can understand a conversation which others can not. 








246 


TELEPHONOLOGY 


Loudness is the test of energy delivered. Clearness is the test of cor¬ 
rect wave form. Up to the present time no instruments have been able 
to measure either of these for the telephone. Loudness may perhaps be 
measured to some extent by the thermal-galvanometer. For clearness 
we must yet depend on the estimates of the ear, though it is not impos¬ 
sible that some means may be worked out to reduce even this to a mathe¬ 
matical basis. It is very desirable that it should be done. 

The parts of a telephone most tested for transmission effects are the 
transmitter, receiver, induction coil, and repeating coil. If it is transmit¬ 
ters that we are testing, one of the number is assumed as a standard of 
loudness and all the others are rated in comparison. It may be that some 



Fig. 306. 

are louder than the standard, in which case they will be more than 1009U 
For clearness, the best method is to take the per cent of words which are 
correctly transmitted by each transmitter. In this case no transmitter 
can have over 100%. 

Fig. 306 gives the arrangement for testing a transmitter in com¬ 
parison with a standard, for both loudness and clearness. The two trans¬ 
mitters are each held separately in a suitable holder, which permits the 
ready change of one for the other or the insertion of any transmitter to 
be tested against the standard. The forked tube is not absolutely neces¬ 
sary, if the tester who does the talking is careful to preserve the same dis- 





































TESTING TELEPHONE PARTS 


247 


cance from the mouthpieces in all the tests. This is especially necessary 
in the tests for loudness, as it is materially affected by the position of the 
speaker’s lips. Care must be taken not to make the tube of tin or other 
metal which will add to the sound spoken by the tester. Its function is 
merely to insure that each transmitter gets the same quality and loudness 
of sound. 

The standard and “X” are in series with each other, the switch, S, 
being provided to short-circuit the one which is not being used. It is the 
main switch used during the test. The battery should be storage cells, 
with the switch, S 3 , to cut in any number from one to three. S 2 connects 
the voltmeter to the transmitter in use or to the battery. The line con¬ 
necting the “A” observer with the “B” observer should be as nearly free 
from distorting influences as possible. This is to place all the burden on 
the transmitter, so that the faults and good points will be the controlling 
features. Theoretically the “B” station needs only a receiver, practically 
it needs also a complete talking outfit so that the two observers can com¬ 
municate about the work. If the sound produced by the transmitters on 
test is too loud, a person can not judge correctly which is louder, so we 
must insert a non-inductive resistance in the line as shown. In order that 
the line shall be free from inductive forces, S 4 is put in to short circuit 
A’s receiver and S 5 to short circuit B’s induction coil secondary. The lat¬ 
ter also cuts out the talking battery. Normally, A does not need to hear 
and B does not need to talk. 


7h TksT 

TRAnSM'TR 

p*. 

C*T. 

STD 

X 

L 0(JD/V£Sb 

£ 

I 

R 

R 

3 A T. £ A\ F 



fiesr 

STD 

rtor 















% Looo/vess 

% 

% 

/Zest 

V 





A 






A 

/*! OT 





a 







Fig. 307. 


It has been found that the ear is better able to judge the comparative 
loudness of two transmitters if words are used with which the listener is 
familiar than if the list of words is changed. In the latter case the ear 
is directing part of its attention to identify the words, and in so doing loses 
part of the effect of the force or intensity. As good a way as any is to 
count from one up to five on each transmitter, switching quickly from the 
standard to the “X” between the last number of one series and the first 
of the next. The observer estimates and records on a prepared form his 
judgment as to the relative loudness of X compared to the standard. If 
X sounds to him a little weaker than the standard, he may record ■ 90%. 
If very much stronger, he may perhaps record 125%. There should be at 
least three readings taken on each transmitter. Then the observeis 
should change places, not knowing what record the other has made, and 
run the observations over again. The mean estimate of the two observers 
should be taken as the true value. After some practice, two men will come 
surprisingly near each other in an unbiased estimate. 






























248 


TELEPHONOLOGY 


It is not enough that this comparison alone be made, for much of the 
value of the test will be lost if certain data about each transmitter is not 
recorded. Records of current, voltage of battery, voltage across trans¬ 
mitter, both at rest and in motion should be made. For this purpose the 
form shown in Fig. 307 may be used. In the upper right hand corner 
record the name and number of the two transmitters. Before beginning 
the test, record the current and voltage for each transmitter on the line 
marked “Rest.” 

Then run through the test, each man filling in his estimates of loud¬ 
ness in the places provided. Then record the battery E. M. F. by throw¬ 
ing S 2 to the lower point. Storage battery should be used so that little or 
no variation will occur. Also the wire connecting the positive end of bat¬ 
tery with the “X” transmitter should be as heavy as convenient, so that 
the IR drop in it will be negligible. The same should be true of the volt¬ 
age taps running to S 3 . This is so that the difference in current taken by 
the two transmitters will not perceptibly affect the battery voltage. To 
get the current and voltage of each transmitter while in motion, the assis¬ 
tance o'* both testers will be required. Let one of them devote himself to 
making a steady vowel sound in front of the tube. The other will read 
the voltmeter and milliammeter. With a little care quite satisfactory re¬ 
sults can be obtained even without having to use a receiver as the exciting 
force. From the various currents and voltages recorded the resistances 
are easily calculated by the application of Ohm’s law. 

The best practical test of correct wave form is the clearness with 
which words are received. Hence the principle of our tests for clearness 
will be the transmitting of a series of words, having a person hear them 
and write them down. The per cent of words correctly received forms 
somewhat of a measure of the clearness of the transmission as a whole. 
This depends on a number of factors. Each part of the apparatus, trans¬ 
mitter, induction coil, line, and receiver, has a part in the matter. The 
line can be eliminated by making it distortionless, that is, without capaci¬ 
ty or inductance. If the line is short and not in cable, it will be practical¬ 
ly distortionless. If resistance coils are inserted, they must be non-induc- 
tively wound. This leaves three factors, transmitter, coil, and receiver. 
How can we test one of them alone without bringing in the faults of the 
others? If we leave the same coil and receiver in circuit and change 
only the transmitter, we may reasonably expect that any variations in 
per cent of words correctly received will be due to that factor which was 
changed. In the ultimate analysis it may be shown that there is a slight 
error in this method, but for practical purposes it is sufficients accurate 
and within the limits of error of the observers. 

For the test prepare a number of lists of words which are of reasonable 
length and in common daily use. Let there be ten words in each list. 
Each observer will prepare the lists which he will read to the other, so 
that the listener will not know what is coming. Reasonable care should 
be taken in reading the words, for there may be as much difference in 
readers as in the apparatus. It is this one fact alone which makes testing 
hard. But with care and practice two men can become sufficiently ex¬ 
pert to get excellent results. In this test the quick change from one 
transmitter to the other is not imperative. It will be well to try several 
lists on each and take the mean per cent. 

The condition of a transmitter is a varying quantity. When new 
and just installed, the granules are loose and the resistance and resist- 


TESTING TELEPHONE PARTS 


249 


ance-change high. As it is used and gets old, the granules have a ten¬ 
dency to pack down, which lowers not only the average resistance but the 
amplitude of change which can be produced by a sound of given intensity. 
Under which condition shall we test our transmitters? Probably the 
fairest to all is to shake each a little just before taking the readings on 
it, in order that it may make the best record that it can. If we were to 
attempt to let them “age” and test them in that condition, it would be dif¬ 
ficult to be sure that they are all in equal condition of aging. And the 
operation of handling them would shake the granules and so destroy, in a 
measure at least, the effect of time. For this reason it is customary to 
agitate each sample just before its test. But it will be well to make some 
tests as to aging, for it is one of the requisites of a good transmitter that 
it shall maintain its effectiveness as long as possible. 



For the comparison of induction coils a slightly different circuit is 
used. Fig. 308 shows how it is arranged. Sj is the main switch, which is 
very conveniently an operator’s ringing key, though it is better if it will 
lock in position like a listening key. A listening key which has inside 
contacts is the best. As be ore, the line should be short and free from 
capacity and inductance. The non-inductive resistance is put in the line 
to reduce the loudness so as to make a comparison more accurate. Its 
exact value must be found by trial. Only one voltage need be taken, that 
of the battery. The current should be the average current during a 
steady sound, in order that some idea may be had of the ampere-turns 
which the coil employs. The different voltages are for the purpose of see¬ 
ing what effect, if any, the current strength has on loudness and clear¬ 
ness. It is quite certain that an increase of current will make both coils 
talk louder, but the question is how it will affect their relative loudness. 
S, and S 4 should be left alone except when necessary to hold conversation 
for directing the work. 

In general the same routine is followed as for a transmitter test. 
Count from one to five on each coil, switching from one to the other be¬ 
tween. This should be repeated often enough for the “B” observer to be¬ 
come sure of his estimate of relative loudness. 

In the test for clearness, use lists of words as before for the trans¬ 
mitter. The same care as to secrecy of lists, care in pronunciation, ex¬ 
change of positions, etc., should be observed. 








































250 


TELEPHONOLOGY 


When it comes to the testing of the receiver, the problem is some¬ 
what complicated by the fact that it is the receiver which we have been 
using to test the other parts. The test for clearness can be made very easi¬ 
ly by using the same transmitter and induction coil and changing receiv¬ 
ers. Use the scheme of lists of words and get the per cent of words 
which are correctly received. But for loudness it is not as easy. We can 
not quickly change from one receiver to another so as to estimate the rel¬ 
ative intensity. Also it is the listener who must make the change and the 
different feeling of a new receiver will throw him off in his estimate. So 
we must look about for some other means. 




Since we can not rely on a quick shift from one receiver to the other 
we must provide some source of current which will be constant at least 
during the test, and devise some means for registering its effect on each 
receiver. Fig. 309 shows one very good current generator which the 
writer has used with the best of success for various kinds of tests. The 
tuning fork is of the electrically self-vibrating type. If it has no device to 
reduce or kill the spark at the contact, the user can shunt the gap with a 
german silver resistance as shown. It should be from 40 to 100 ohms re¬ 
sistance, depending on the voltage necessary to run the fork. The higher 
voltage will require the higher resistance. For average current, shunt 
the primary of a local battery induction coil around the working coil, R 1 , 
of the fork. Since the resistance of the primary winding is low, a con¬ 
denser must be inserted as shown, C\ to prevent the shunt from robbing 
the working coil of current. 

When the contact of the fork closes, the battery current rises in R 1 
and attracts the prongs of the fork. This rise of current in the working 
coil, R,, causes a rise in the voltage at its terminals. This charges the 
condenser, C,, to flow out. In flowing out it passes through the induction 
coil in the opposite direction from what it did in flowing into the conden¬ 
ser. This continued action causes an alternating current in the primary 
winding, which induces an alternating current in the secondary. If a 
weak testing current is desired, the induction coil can be reversed, putting 
the secondary next to the working coil. This is also shown in the figure. 
It now acts as a step-down transformer. 

If stronger current be desired than can be furnished by either of the 
above arrangements, the scheme shown in Fig. 310 may be used. It con¬ 
sists in placing the primary of the induction coil in series with the main 
circuit, so that it will get the full benefit of the current-change. 












































TESTING TELEPHONE PARTS 


251 







One means for testing the loudness of a receiver consists in passing 
through it a standard current and holding it away from the ear till the 
sound is just audible. Measure the distance. Then let the receiver, ap¬ 
proach the ear till the sound is just audible. Take the distance again. The 
mean of the two distances will be a measure of the intensity. If we com¬ 
pare several receivers by this method, we shall be obliged to compare their 
intensities by taking the law of sound into account. This law is that the 
intensity varies inversely as the square of the distance. Let us state the 
law mathematically. 

< -d, • 

X 

F/G:3II 

* - <*i 


Let the unit source of sound be that source which will produce unit 
loudness of sound at unit distance. 



Let k = measure of the intensity of the source of sound, 
d = distance from the source to the ear. 
s = loudness of sound as heard by the ear. 


In Fig. 311, let X represent the source of sound and 0 the position 
of the ear of the tester. If the intensity of the source is k, and the dis¬ 
tance to the nearest point d„ then the intensity of sound observed at that 
point will be 


k 

(1) s, = -* 


Similarly, the intensity of sound received at the farther point will be 

k 

(2) s„ - - 

d% 

If we have tested two receivers by the method outlined above, see 
Fig. 312, we have found that the vanishing point for the standard receiv¬ 
er is d. Call its intensity as a source of sound k,. Let the same data for 
the “X” receiver be d 2 and k 2 . Treat the standard receiver as unit 
source since we have no standard by which to measure it. Then all that 
we can do is to get the ratio between the two “k values. Since the dis¬ 
tances determined are for the vanishing points of sound, the intensity of 
sound received is the same. That is, 

s, = s 2 

and we can at once write the equation 


k, k 2 


k 2 





( 3 ) 


so that 


















252 


TELEPHONOLOGY 


The above is the same as saying that the loudness of the unknown re¬ 
ceiver measured in terms of the standard is obtained by dividing the 
square of the vanishing distance for the unknown by the square of the 
vanishing distance for the standard. 

In making the test two persons are necessary, one to listen and the 
other to manipulate the apparatus. It is essential that the listener shall 
not know what is happening except as he can hear it. He should not 
know which receiver is being tested, nor the point at which any sound 
vanishes. This will keep his mind free from insensible prejudice, whicn 
is sure to creep in if not guarded against. 

Another method which is believed to be better has been devised by 
the author. The method of the vanishing point is subject to considerable 
error from the fact that very slight causes interfere with it. A slight 
noise in the room makes it hard for the listener to tell when the sound has 
ceased to be audible. Training enables him to hear at a greater distance 
than at the start of his work, so that considerable time is lost in getting 
the ear up to its maximum sensitiveness. It is an aid in finding the vanish¬ 
ing point if the testing current be intermittently cut off from the receiver 
under test. But with all precautions, it is not a very satisfactory way. It 
has been found that the ear is better able to judge the equal loudness of 
two sounds than the vanishing point of either of them. This is specially 
true if the sounds are not too loud. Fig. 313 gives the outline of the au¬ 



thor’s method. At one end of a suitable scale is arranged a place for the 
listener’s ear, which must not be in contact with the scale. At the point 
on the scale which is 100 divisions from the “0” end is placed the receiver 
which is to serve as the standard. The unknown receiver is mounted on 
a sliding carriage, which can be moved along the scale. Both receivers 
have their openings directed toward the zero end of the scale. The two 
are wired in series with each other, and have a switch, S, which can short 
circuit either at will. A non-inductive resistance is put in the circuit to 
the tuning fork to prevent the sound from being too loud, also to keep the 
current as nearly constant as may be. In working with receivers of dif¬ 
ferent makes, the resistances and inductances often vary considerably. 
If the resistance of the circuit is low, the receiver which is un¬ 
der test i forms quite an appreciable part of the total. If we now shift to 
the other receiver with its higher or lower impedance, the current will be 
changed in consequence. This will vitiate our results, as we are com¬ 
paring the receivers on the basis of equal current. If sufficient non-in¬ 
ductive resistance be inserted, the change from one receiver to the other 
will not perceptibly affect the current strength. This same resistance 
will also enable the operator to adjust the loudness to the best degree for 
estimating equality. 











TESTING TELEPHONE PARTS 


253 


In using, X is first slid back till there is no doubt of its sound being 
weaker than that of the standard. This is determined by working the 
switch which cuts out either receiver. Then move X slowly closer to 0 
till the listener can tell no difference between the loudness of the two. 
Record the scale reading. Then slide X up till its sound is very much 
louder than that of the standard, and slowly slide it back till the two 
sounds are again equal. Record this point on the scale. These two scale 
readings should be not far from each other, and if so take their mean. If 
the position of the standard is marked 100, point off two places from the 
mean reading of the unknown and square it. 

Suppose the two readings of the X receiver are 110 and 116. The 
mean is 113. Point off two places, giving us 1.13. Square this, giving us 
1.2769 as the intensity of X with respect to the standard. This simplifi¬ 
cation of ormula (3) comes about by making the distance, d lf equal to 
imity. Although marked 100 on the scale, it becomes one by pointing off 
two places. If desired, the scale may be graduated in squares, so that the 
intensity can be read off at once. Below is given a list of a few points on 
the scale to show how it will appear if graduated in squares. 

Unit’s Scale 0 .25 .50 .75 1.00 1.25 1.50 

Squares 0 .0625 .25 .5625 1.00 1.5625 2.25 

There are two other methods, both depending on finding a vanishing 
point, which may well be mentioned. One of these is illustrated by Fig. 


n l , 1 . 1 

---> 

7s sr 

Ct/*/*c/vr 

1 i 1 i 1 i 1 i 1 i 1 i 1 t 1 i 1 i 1 i/"i ■aa/'AaAAA-- 


S<./P£ kv/Si £. 


1 /7^3/5: 



1 


314. C, and C„ are two coils of wire of the same dimensions, resistance, 
turns, etc. Each is wound on a wooden or other non-magnetic frame. C, 
is fixed at the zero end of the scale with its plane at right angles to it. The 
other coil, C.„ is mounted so as to slide along the scale and is parallel to 
the first coil. An alternating current in the stationary coil will induce a 
voltage in the moving coil, and the magnitude of the induced voltage will 
depend on the distance between the two coils, the current in C, being con¬ 
stant. If any receiver be attached to C, a current will flow in it, making 
a noise. In a certain way the distance between the coils when this noise 
vanishes is a measure of the sensitiveness of the receiver. It is open to 
the objection that different makes of receivers have different resistances 
and inductances and the currents will not be equal under equal voltages. 
This may be to some extent overcome by inserting a non-inductive resis¬ 
tance in series with the receiver as in the second method described. This 
may require a stronger testing current in C,. 








254 


TELEPHONOLOGY 


The other of these last two methods employs a slide wire and resis¬ 
tance in connection with the testing current. Fig. 315 shows the scheme 
of the connections. The resistance, R, merely regulates the flow of cur¬ 
rent so as to enable the observer to bring the vanishing point at any de¬ 
sired place on the wire. The portion of the slide wire between the stylus 
and the end to which the receiver is attached acts as a shunt to the re¬ 
ceiver. As the stylus is moved to the left the sound diminishes till it can 
not be heard. This point is marked. Then the stylus is moved to the 
right till sound first appears and another reading taken. The mean of 
the two is taken as a measure of the receiver. In this test, the loudest 
and best receiver in this respect will be the one which will stand the 
greatest short circuiting before the sound vanishes. Therefore, the meas¬ 
ure is inversely as the length of the shunt or the reading on the wire, if 
the reading for the standard receiver is 50 and for the unknown 65 then 

X 50 

_ — _ — .77, 

Std. 65 

which means that the X receiver is weaker than the standard. ; 



r^< 




:- U/ WW 

"V/ wirnour *4 

OUTORT/OA/. 



In testing repeating coils, we have two things to consider. If it is a 
ring-through coil, both ringing and talking must be tested. Some coils 
are for talking only and will not need the ringing test, though it is often 
interesting to see what such coils, will do. Fig. 316 shows an arrange¬ 
ment for repeating coil testing for talking efficiency. K, is the main key, 
for it switches from the standard to the unknown or X coil. It is a 
double throw key, locking in both positions. As wired for this test the 
lever must be either at the extreme right or extreme left. R, and R 4 are 
non-inductive resistances in the line to control the conditions. A repeating 
coil is called on to act under two trying conditions, repeating a weak cur¬ 
rent from a long line into a short line, and the reverse, repeating a strong 
current into a long, high resistance line. The proper use of S 1 and S 2 will 
give these conditions. Further directions are hardly necessary, as the 
tests for loudness and clearness are to be conducted as directed for trans¬ 
mitters and induction coils. 

For a power test of a repeating coil, the most thorough would include 
the total power in watts required to operate it under various loads, the 













































TESTING TELEPHONE PARTS 


255 


analysis of this power into copper loss and core losses, also the determin¬ 
ation of inductance, mutual inductance, and angle of lag at various loads. 
In addition the curve of regulation on the secondary side would be needed. 
Although all of this data can be very nicely obtained by the use of the 
Rowland Electro-Dynamometer, it is usually more elaborate than would 
be required in any case except the advance research. There is one test 
with the above named instrument which I shall give as worthy of a per¬ 
manent place in the list of tests which will throw great light on the per¬ 
formance of this very needful apparatus. 

The theory of the method for getting the external characteristic curve 
of a repeating coil is shown in Fig. 317. V, and V 2 are two voltmeters, 
taking the voltage of the primary and secondary windings of the coil un¬ 
der test. and A., are ammeters taking the current in each circuit at 
the same time. The load resistance is started at an open circuit, or in¬ 
finity. It is decreased by suitable steps till the load is heavier than there 
is any possibility of its being in service. Two curves are then plotted, 
each by laying off on the base line (horizontal line or line of abscissse) the 
current values, and at each point erecting a vertical line corresponding 
to the voltage for that current value. The curve is drawn through the 
points thus plotted. 




The ordinary alternating current voltmeter is not suitable for this 
work as its resistance is far too low and introduces more load on the coil 
than several bells. Ordinary alternating current ammeters usually have 
too much internal resistance in the lower ranges and introduce too much 
error. The Rowland dynamometer can be arranged to possess these errors 
in a slight degree which may be neglected. Since four instruments would 
be too expensive it is necessary to have some switching device which will 
quickly shift the same instrument from one position to another. The 
same one has connections for both current and voltage readings. In r ig. 
318 is shown the circuit for accomplishing this result. 

The dynamometer is represented by a large circle for the stationary 
coil, a small circle within it for the hanging coil, and the two resistances 
with the regular symbols. *See foot note. 

K, is the key which throws the instrument into either circuit. K 2 
changes the connections from current to voltage readings, while K 3 con- 

*For further information concerning the Rowland Dynamometer and its uses the 
reader is referred to the makers, Leeds & Northrup Co.. Phila. Pa., also the writings of 
Henry A. Rowland, and an article by the same in the Am. Journal of Science for Dec. 
1897. entitled “Electrical Measurements by Alternating Circuits." 

















































256 


TELEPHONOLOGY 


nects the high resistance to the proper coil which is being measured. In 
its normal position, K x leaves the circuits free from all apparatus. 

To measure current in the secondary, it is only necessary to throw k,, 
to the “S” position, leave K 2 normal, and make the necessary adjustments 
of the dynamometer. To take voltage, throw K.,, having previously put 
K, on “S,” and make the proper adjustments of the instrument. At all 
times care must be taken to make such adjustments of the dynamometer 
proper as will result in the highest possible resistance in the “voltage re¬ 
sistance.” Also when measuring current, such combinations of the in¬ 
strument should be used as will give the lowest resistance. These precau¬ 
tions are to avoid disturbances from the introduction of the measuring in¬ 
strument into the circuits. 

The form of the resulting characteristic curve will be as shown in 
Fig. 319. The more level the line, the better the coil holds up under load. 
Curve I shows a coil which has less internal losses than the coil which 
gave Curve II, although the voltage on open circuit was lower for the 
former. The study of a set of such curves is very interesting and will 
show up the capabilities of coils in a way which permits close comparison 
of coil with coil. 




A simple method of testing the ringing ability of a repeating coil is 
shown in Fig. 320. The only materials required are a generator, two re¬ 
sistance boxes, a simple two way switch, a bell, and the coil to be tested. 
It is best to have some power generator to furnish the current, as it will 
be much more likely to be steady than a hand generator turned by hand. 
But if care is taken to turn with uniform speed, even a hand generator can 
be* made to give excellent results. If a pole-changer is the source, it will 
be necessary to do the testing when the machine is idle, for when an ope¬ 
rator rings out on a line, it lowers the terminal voltage materially. Let 
L represent the line resistance and R a leak across the line. Start witli 
the line resistance equal to two or three hundred ohms, and reduce the 
leak till the bel] will just ring reliably. Record the resistance. Then make 
the leak so low that the bell will not ring and increase it till it will just 
ring reliably. The mean between the two will be a good value for the 
limiting leak whichi may be operated with that certain line resistance. 
Now increase the line resistance, making it a hundred ohms higher than 
before. In the same way find the limiting leakage resistance which will 
ring the bell. Continue in this way till the line resistance has been raised 
to about 2000 or 3000 ohms. The completed records will give us a series 
of line resistances with the limiting value of leak for each. These may 
be plotted iti the fofm of a curve, laying out the line resistances horizon¬ 
tally and the leakage resistances vertically. By plotting the results of 
several coir tests on the same sheet, it will readily be seen how their per¬ 
formances compare. The coil which will on a given length of line ring 
















TESTING TELEPHONE PARTS 


257 


the bell past the lower leak, is the one which will under trying conditions 
be more sure to ring the bells on a line. 

Care should be taken to use the same generator in testing a series of 
coils, for if different machines are used, their differences in voltage will 
lead the experimenter astray. If desired, a common switchboard drop 
may be substituted for the bell, but there is a possibility of uneven action 
due to friction at the shutter at the moment of starting to ring. The bell 
should be the same for all the tests, and should be in the same position. 

A good check test is to exchange the positions of the bell and gen¬ 
erator. This gives the condition of a subscriber ringing in to central 
through a repeating coil. 

The curve shown in Fig. 320a was taken in the above manner from 
a ring through repeating coil. Curve No. 1 shows the result when the 
leak on the line is beyond the line resistance. Curve No. 2 was taken with 
the leak on the near side of the line resistance. These show how much 
more effect a leak produces when it is out some distance from central. In 
other words, the line can stand a worse short circuit near the coil, than it 
can some distance away. It also shows up the great ability of the coil to 
furnish large current without pulling down its voltage. 



Fig. 320a. 

Testing Magneto Generators —A magneto hand generator such as is 
commonly used for ringing on telephone lines is as much a dynamo as any 
machine, and can be tested as such. But owing to the peculiarity of hav¬ 
ing a permanent field it does not behave in the same way. Also on ac¬ 
count of using a shuttle armature, the core of which is usually solid iron, 

17 



















































































258 


TELEPHONOLOGY 


not laminated in any way, the power losses are much greater than in or¬ 
dinary generators. This is heightened by the voltage required, which is 
out of proportion to the size of the machine. This makes many turns of 
small wire necessary, which increases the internal losses. But we are not 
hampered by considerations of efficiency as much as the power people, for 
if a generator will do the work required it will be satisfactory, provided 
it does not turn unreasonably hard. It is very likely that less than half of 
the energy expended by the subscriber in turning the crank goes out in the 
form of electrical energy over the line. But efficiency does come in 
wherever we can reduce the size and cost of a machine, and yet be as ef¬ 
fective in the work. 




The most thorough test which is ordinarily applied is to take the 
external characteristic. This is merely the curve of terminal voltage and 
current delivered to a non-inductive circuit. Fig. 321 shows the theoreti¬ 
cal arrangement. The crank is taken off and replaced by a driving pul¬ 
ley, so that a motor, or any source of power can drive it at a uniform 
speed. The voltmeter and ammeter must be adapted for alternating cur¬ 
rent. The resistance of the former should be as high as possible. I have 
found the Rowland Dynamometer the best for the purpose, both as volt¬ 
meter and ammeter. The ordinary voltmeter for alternating current has 
too low resistance. 

For taking the speed, the arrangement shown in Fig. 322 has been 
tried out with the best of success. Fitted to the driving pulley is a seg¬ 
ment, S, which is connected to the shaft. A brush, B, is adapted to touch 
the segment once in each revolution and close the circuit through the mo¬ 
tor magnet,MM, of a step-by-step device which is in the figure called the 
“selector.” In my own use I have employed the switch from a Clarke au¬ 
tomatic telephone switchboard, as it makes a complete circle in its rota¬ 
tion. The motor magnet drives the wiper over a series of contact points, 
one of which, P, is wired to a telegraph sounder. The return circuit for 
the sounder is through battery to the wiper. The use is as follows: The 
wiper is set on the point, P. When ready to take the speed, the key is 
closed for one minute, or some definite time. Every revolution of the 
driving pulley closes the motor magnet circuit once, moving the wiper 
forward one point. Once in each revolution of the selector the sounder 
will click. By counting the number of clicks in a minute and multiplying 
by the number of points in the complete revolution of the wiper and add- 

































TESTING TELEPHONE PARTS 


259 


ing the number of points over which the wiper has run past the point P, 
you can get the revolutions per minute of the driving pulley. Knowing 
the ratio between the small and large gears, the actual frequency of the 
armature is easily computed. The best frequency for hand generators is 
from 16 to 20 cycles per second. 



The procedure is very similar to that for testing repeating coils 
which has been previously described. The open circuit voltage is first 
taken with the resistance infinity. Then the load is applied to the extent 
of a few milliamperes, and the voltage taken again. The load is increased 
a few more milliamperes and another voltage reading taken, and so on till 
a reasonable limit has been reached. In most hand generators the curve 
will very closely approximate a straight line for some distance, after 
which there may be a slight bending downward. The working load 
should come within the straight portion of the curve. Fig. 323 illustrates 
the form of the curve. The straight part indicates that the current is not 
large enough to have a perceptible effect on the magnetism of the steel 
magnets. The bend downward at P is caused by the large current in the 
armature, which tends to destroy the magnetic field set up by the steel 
magnets. The slope of the straight part of the curve is an indication of the 
electrical losses in the armature. If the line is almost horizontal, the 
losses are small, but if the line is steep, the losses are large. 



Current R'ejfectirt 

Resistcuct 


Let E = open circuit E. M. F. (when current = zero.) 

e = terminal voltage at some selected point on the curve. 
I = current corresponding to voltage “e.” 

R = internal resistance of armature winding, 
f = frequency, in cycles per second. 

Z = impedance of armature. 































260 


TELEPHONOLOGY 


Then e -f- IR = volts in phase with current. 27rfLI = reactance 
volts. 

E L = (27rfLI) 2 + (e -f IR) 2 . Solving for L, we may get the for¬ 
mula for computing the inductance of the armature. 

V E 2 — (e + my 

L = - 

2^fl 

The impedance, 2, of the armature is given by 

2 = VR 2 + ( 27 rfL ) 2 

In that portion of the curve which is a straight line, the impedance, 
Z, and the inductance, L, will be constant quantities. In a certain old 
style hand generator which was tested, the following values were found, 

E — 63, e = 22, I = .05 amp., R : 515, f : 20. 

This gave an impedance, Z, of 955 ohms, and an inductance, L, of 6.4 
henrys. The electrical efficiency was 46 per cent. 

Hand generators may be tested for their ability to ring a bell over long 
lines past leakage in exactly the same manner as was described for ring 
through repeating coils. See Fig. 320 and 320b. The difference between 
the curves for leakage on either side of the line resistance will give evi¬ 
dence of the amount of internal losses in the armature. 



Poiver Consumed by Polarized Bell .—The following are some resuts 
which were obtained on a bridging bell. They do not give the least 
amount of power on which the bell will ring, but show where the power 
goes to in the average case. The measurements were made with the Row¬ 
land Electro-dynamometer, for current, voltage, and watts. Briefly the 
method was this: Measure the current going into the bell, and the volt¬ 
age across its terminals. Measure the watts consumed by the bell. Meas¬ 
ure the resistance of the coils by a Wheatstone bridge. Find the appar¬ 
ent power by multiplying the volts by the current. Divide the real pow¬ 
er, given by the watts, by the apparent power. The quotient is the power 
factor, or the cosine of the angle of lag. By this cosine lay off the angle 
by which the current lags behind the voltage. See Fig. 324. Divide the 







































TESTING TELEPHONE PARTS 261 

volts by the current, which will give the impedance. Lay off the value Z 
of the impedance on the sloping side of the angle. From the end of the 
distance representing the impedance drop a line perpendicular to the base 
or horizontal line. This length will represent the reactance, x, which 
equals 2-k fL. f is the frequency and L is the inductance. The horizontal 
distance represents the effective resistance, not the resistance of the wire 
in the coils, but nearly always greater, due to the losses in the iron core. 
In the following table of results, Set. 1 and Set. 2 differ only in the volt¬ 
age applied, but it shows that the change in voltage affects other things as 



Fig. 324a. 


Resistance of bell, 1560 ohms, Frequency, 18 cycles per second. 

Set. 1. Set. 2. 


Current 
E. M. F. 

Power, total. 

Angle of lag. 

Impedance 
Reactance 
Effective resistance 
Inductance 

The above results were 
were calculated by the above 


.01133 amp. 
80.384 volts 
.5849 watts 
50deg. 2' 
7090.4 ohms 
5434.1 ohms 
4554.8 ohms 


.01017 amp. 
70.144 volts. 
.4602 watts 
49deg. 46.5' 
6897.1 ohms 
5265.0 ohms 
4454.0 ohms 
42.67 henrys 


44 henrys 

not worked out on the drawing board, 
mentioned relations. 


but 


In telephone work alternating and intermittent currents are dealt 
with and consequently the simple direct current relations fail in any com¬ 
putation or test on the telephonic apparatus. 

As in direct or continuous current work the ohmic resistance offers the 
opposition to the passage of the current, so in alternating or intermit¬ 
tent current work the impedance opposes the passage of the current. The 
part of the impedance that plays the most important role in telephonic 
work is the induction in the receivers, ringers, induction or loading coils, 
etc. 

To measure the inductance in these, by far the simplest method is to 
compare them directly with standards of induction in a manner similar to 
that used in the comparison of resistances. Such a method has, in ad¬ 
dition, the advantage of being a zero method, namely, the inductances are 
balanced until there is no deflection in the galvanometer. 













262 


TELE PHONOLOGY 


To make these measurements it is necessary to have standards of in¬ 
duction o f various values and a variable standard that can be increased or 
decreased by small amounts. 

Fig. 324a shows a box form of fixed standards which is particularly 
adapted to this purpose, as the resistance remains the same whatever in¬ 
ductance is plugged in or out. (As indicated below, it is necessary that 
the resistance of the circuit must remain the same while a test is being 
made.) 



Fig. 324b. 

Fio-. 324b shows the highest standard type of variable inductance 
which indicates values below the smallest values given in the box shown 
in Fig. 324a. The important feature of this variable standard of induct¬ 
ance is its solid and rigid construction. The accuracy of the whole instru¬ 
ment depends upon its maintaining a permanent shape and must not be 
liable to warp or twist with time or under varying climatic conditions. 

An important adjunct in measurement is a Secolimmcter or instru¬ 
ment for converting a steady or direct current to an intermittent one. 

Fig. 324c show such an instrument designed for the purpose, with 
special attention given to the reliability of the contacts and the strength 
and smoothness of the gears. 




















TESTING TELEPHONE PARTS 


263 


To illustrate the use of these instruments the diagram (Fig. 324d.) 
will show the connection necessary to make a test of the induction of any 
part of the telephonic apparatus. 

To illustrate the use of these instruments the diagram (Fig. 324d.) 
as shown above, R 4 and R, are known non-inductive resistances; L 2 R_, 
is a fixed standard of inductance; L 3 R., is a variable standard of induct¬ 
ance; R- R s is a wire giving smaller variations of resistance than the 



Fig. 324c. 


smallest coil in R r> ; R (i is a non-inductive resistance. Having the Secohm- 
meter S,, S„ at rest with the circuits complete through the commutators, 
make a balance between R 4 , R 5 , R, -f R„ + R,„ and R._, + R 3 + ior 
zero deflection of the galvanometer as in an ordinary resistance measuie- 
ment. L, R., is not needed when L, is less than the maximum value ot L . 
R 0 is used to' produce a balance of resistances and is placed between L, and 
R. or L 3 and R 7 according as R 4 is smaller or greater than R 2 + R 3 . 



Slowly turn the Secohmmeter and vary L._, and L :1 until there is again 






















264 


TELEPHONOLOGY 


When a box like the one shown in Fig. 324a is used for L 2 the resistance 
remains contant, however L 2 is changed. 

When the balance of inductances is obtained as above, rotate the Sec- 
ohmmeter rapidly and make the final adjustment for zero deflection with 
L 3 , then L x is found from the following relation: 

R 4 


+ ^3 R 5 

Cautions. The resistance boxes used should be non-inductive and 
free from capacity, and therefore the individual resistance arms should 
not be under 100 ohms and of large wire. 

All connections should be as straight as possible. 

Foreign magnetic material or strong currents should not be near the 
apparatus when a test is being made. L 2 , L,, and L 4 should not be too 
near one another. 

All contacts and connections should be good. 

As this method depends entirely on the accuracy of the standards, it 
is well to observe that they are reliable. 



CHAPTER IX. 


TESTING EQUIPMENT AND FAULT LOCATION. 


The question of Portable Testing Set and Cable Testing apparatus 
equipment for the maintenance of tests upon telephone lines is of prime 
importance. A telephone plant can only give best service when its lines 
are clear of all troubles. In the light of the present day engineering we 
must not wait until a fault develops, but must be in a position to foretell 
such conditions by systematic tests, or if crosses and grounds develop due 
to agencies beyond our control, we must have the necessary apparatus to 
locate these troubles promptly and accurately. 

The selection of a testing set will depend upon the range of the test¬ 
ing to be done, and the views of the tester, as to the details of construc¬ 
tion and manipulation, or the experience of the manufacturer may be 
sought for recommendations of apparatus to meet particular require¬ 
ments. In choosing an instrument, the importance of reliability must not 
be overlooked. This factor is dependent upon the manufacturer, who 
must insure reliability by good construction. It is a common error to se¬ 
lect cheaply constructed apparatus, which while giving results sufficiently 
accurate for many cases of cable and line trouble, has a short life and 
must be replaced. Another feature of this class of apparatus is failure to 
operate at a time when a critical test is to be made. The wisdom, there¬ 
fore, of selecting testing sets, that are constructed so as to withstand the 
rough usage to which this class of apparatus is subjected and that have a 
construction and adjustment which will insure reliability and accuracy, 
is self-evident. 


PORTABLE TESTING SETS. 

Definition .—The term “Portable Testing Set” is now accepted to mean 
some form of Wheatstone or Slide Wire Bridge, complete with galvano¬ 
meter and battery, mounted in a carrying case and arranged for the 
measurement of resistances and the location of faults, crosses and 
grounds by the Murray and Varley Loop Methods. The same set with the 
addition of other parts can also be arranged for additional tests, but as 
will be shown later, such tests are only rough, and when precision is re¬ 
quired should be made with the instruments included in cable testing ap¬ 
paratus. 

Explanation of Wheatstone Bridge .—As stated above all test sets are 
arrangements of the Wheatstone and Slide Wire Bridges. In order to un¬ 
derstand the principles of a bridge arrangement, a discussion will be 
given. 


( 265 ) 




266 


TELEPHONOLOGY 


The Wheatstone Bridge is named after Sir Charles Wheatstone, to 
whom we owe its development although invented by Christie. It consists 
of a system of conductors as shown in Fig. 325 and is the most common 
of the several arrangements used for measuring resistances. 

The current from the battery C is made to branch at 2 into two paths 
and reunite at 4, so that part of the current flows through the point 1 and 
part through the point 3. The four parts of the circuit A, B, R and X are 
known as the arms of the bridge, although it will be stated later that in 
practice A and B are termed the “Bridge Arms” or “Ratio Arms,” R the 
“Rheostat” and X the “unknown resistance” or “bridge terminals.” 

When the resistances in the four bridge arms bear a certain relation 
to each other, then the galvanometer connected at 1 and 3 will show no de¬ 
flection or a condition of “balance,” in which case the bridge is said to be 
“balanced.” 




Fig. 326. 


It is to be noted that any resistances in the galvanometer or battery 
circuits do not affect the values or ratios of the bridge arms. It is also 
to be noted that the position of the galvanometer and battery may be in¬ 
terchanged without in any way affecting the law of the bridge. There are 
certain conditions of use which may require the galvanometer connected 
from 2 to 4, but this discussion will not be entered into since it does not 
alter the law of the bridge. 

Portable Testing Sets, making use of the Wheatstone Bridge prin¬ 
ciple, are all connected according to the theoretical diagram shown in Fig. 
325. The method of adjusting the bridge, so as to obtain a balance, is to 
vary the arm R or Rheostat, the arms A and B having been set for fixed 
values depending upon the resistances to be measured, or to vary the ra¬ 
tio of the bridge arms in relation to a fixed rheostat. The first method is 
employed in the post office and decade bridges and the second method in 
bridges of the slide wire type. The arrangements of the various parts 
are the result of practice and experience in the use and design of this 
class of apparatus. 

The various typical forms to be found in practice will be illustrated 
and their methods of operation described. 

The Portable Testing Set shown in Fig. 326 is the simplest form of 
Wheatstone bridge and is known as the “Postoffice” pattern. This name 
is derived from the fact that the general construction was first gotten out 











TESTING EQUIPMENT AND FAULT LOCATION 267 

by the department of telegraphs of the English government, which is un¬ 
der the supervision of the postoffice. 

It is conveniently portable and is used for measuring resistances, 
ranging from a fraction of an ohm to a few megohms. It is also ar- 
langed for the location of faults, crosses and grounds by the Murray and 
Varley Loop Methods. 

Reference to Fig. 327 shows the Rheostat or variable arm of the 
bridge to consist of resistances from 1 ohm to 4000 ohms. The bridge 
arms have each three coils, 1, 10 and 100 ohms in one arm and 10, 100 
and 1000 ohms in the other arm. These resistances are wound with Man¬ 
ga™ 11 wire, which is an alloy, having a very low temperature co-efficient. 
Resistances wound with this metal require no temperature corrections. 



Fig. 327. 

The galvanometer is of the D’Arsonval type and is therefore un¬ 
affected by external magnetic influences such as dynamos or the earth’s 
magnetic field. It is designed so as to give a maximum sensibility and be 
at the same time deadbeat and quick in action. It requires no suspending 
or leveling. 

The battery is composed of small dry cells having a high voltage and 
low internal resistance. They are mounted in a block which can be re¬ 
placed when the cells are exhausted. A pair of binding posts is provided 
so that outside battery may be used. 

The arrangement and connections are shown in Fig. 327. The dotted 
lines show internal connections. It will be noted that the arms A and B 
are not directly joined to each other as indicated in the theoretical dia¬ 
gram, Fig. 325. but are connected to a commutator, Fig. 328, so that the 
relative position of the arms A and B may be interchanged. The object 
of reversing the bridge arms is to give the most accurate measurement 
for certain values of the unknown resistance. This increased accuracy 
of measurement is in some cases so marked as to warrant care in select¬ 
ing the bridge arms. 

The transposing of the bridge arms must necessarily invert their ra¬ 
tio to each other. The upper block in the commutator is permanently con¬ 
nected to X, and the lower block of the commutator is permanently con¬ 
nected to R. If therefore it is desired to connect either bridge arms to X 
or R, it is only necessary to place the two plugs accordingly. 






























268 


TELEPHONOLOGY 


Fig. 329 and 330 give the formula for the unknown resistance when 
the bridge arms are connected as indicated. It will be noticed on blocks 
X and R that there are also the small letters D and M. These stand for 
divide and multiply. They are to serve as a guide in placing the plugs. 
When the plugs are placed on the diagonal D D the rheostat reading is to 
be divided by the ratio A-f- B, when on the diagonal M M it is to be multi¬ 
plied by that ratio. 



Directions for using the Post Office Bridge , shown in Fig 326, for the 
Measurement of Resistance. —Referring to Fig. 328 the unknown resis¬ 
tance X which is connected between the binding posts X 1 and X 2 , is de¬ 
termined from the proportion B : R :: A : X whence 

A 

X = R —. 

B 

The proportion obtains, when with the battery current flowing the resis¬ 
tances are so adjusted that no current flows through the galvanometer. 
Assuming that nothing is known about the resistance to be measured, 
proceed as follows: Place battery plug in position, connect the unknown 
resistance between X 1 and X 2 , unplug 100 ohms in bridge arm A and 
bridge arm B. Connect block R^ to block G and block R 2 to block Ba 1 , and 
see that all other plugs in both bridge arms and the rheostat are firmly in 
position. Unplug a coil in the rheostat, 1,000 ohms for example, and close 
the battery key and immediately afterwards tap the galvanometer key; a 
deflection in the direction of the arrow would indicate that more resistance 




















TESTING EQUIPMENT AND FAULT LOCATION 

was to be unplugged, and in the oppositie direction, less. Bearing this in 
mind a value will be determined by successive trials which will give a bal- 
will be discovered that the unknown resistance is greater than 
11,000 ohms, or less than 1 ohm, these being the limiting values of meas- 
urement when th6 same resistance is unplugged in each bridge arm For 
many resistances an even bridge does not give the best results. 



Fig. 329. 




Fig. 330. 


Fig. 331. 


Best Values. —The best bridge values for each measurement may be 
obtained from the following table: 


Below 10 ohms 
10 ohms to 
100 “ 

500 “ 

50000 “ 

50000 “ 
500000 “ 



1 

1000 

100 ohms 

10 

1000 

500 “ 

10 

100 

5000 “ 

100 

100 

5000 “ 

100 

1000 

500000 “ 

10 

1000 

11000000 “ 

1 

1000 


D D divided by 1000 

D D “ “ 100 

D D “ “ 10 

either 

M M multiply by 10 
M M “ “ 100 

M M “ “ 1000 


When making resistance measurements, it will often be found that 
an exact balance cannot be obtained. The galvanometer will deflect to the 
one side of zero, with a certain resistance unplugged in the rheostat and 
then to the other side, when the next resistance value is unplugged. In 
order to make a measurement to the highest degree of precision within 
the limits of the particular bridge in use, we resort to interpolation or the 
determination of the ratio of the galvanometer deflections on each side of 
zero to the resistances unplugged to produce these deflections. 

An example will make this operation clear. In the measurement 
of an unknown resistance it is found that the needle swings with the ar¬ 
row when 11 is unplugged in the rheostat and against it when 12 is un¬ 
plugged, and there is a considerable swing in each direction. Noting the 
amount of the deflection we find that the needle swings .4 division from 
zero when 11 is unplugged and .2 division when 12 is unplugged. The 
proper value is consequently nearer to 12 than 11, and in the proportion 
2 to 4; we accordingly annex 4-6 to 11, making our rheostat reading 11.7. 

If the unknown resistance in the above example had been below one 
ohm, then we would have unplugged 1 ohm in B and 1000 ohms in A and 
set the commutator plugs on D D. The final result therefore would have 


l 


























270 


TELEPHONOLOGY 


been 11.7 divided by 1000 or .0117 ohms. In the measurement of a low 
resistance, precaution should be observed to close the galvanometer key 
first and keep the battery key closed as little as possible. As the battery 
is short circuited through a small resistance in all these measurements, it 
will be used up unnecessarily if this precaution is not observed. 

The “Decade” Wheatstone Bridge .—The portable testing set just de¬ 
scribed was termed the “Postoffice” pattern, and in order to obtain a re¬ 
sistance value in the rheostat or bridge arms, it is necessary to withdraw 
a plug. 

In the Decade form of bridge the resistances are obtained by “plug¬ 
ging in,” and furthermore but one plug is required for each row of resis¬ 
tances in the rheostat. 

A testing set arranged on the “decade” plan is shown in perspective 
in Fig. 331, and in plan in Fig. 332. The advantages of the “decade” plan 
over the “postoffice” plan are numerous and especially so from the stand¬ 
point of manipulation. It requires but one plug for each row of resis¬ 
tances and this plug is always in use, even at zero it must be in its posi¬ 
tion. In the “postoffice” type it is necessary to withdraw plugs and lay 



Fig. 332. 


them aside, thereby bringing in the possibility of loosing them. The use of 
one plug only to the decade makes it easy to ascertain that this plug is 
tightly fitted in its place and making good contact. As only one block in 
a row is plugged at a time, the other blocks are not kept under a strain by 
having plugs tightly forced between them. This strain on the blocks, 
which always exists in the postoffice type in which a resistance is thrown 
in by removing a plug, tends to separate or loosen them. This trouble 
must be guarded against in the postoffice type by running over all the 
plugs, to see that they are tightly in position, just before making a meas¬ 
urement. Reference to Fig. 332 will make it evident that on account of 
the ample distance between the rows, there is no trouble in manipulating 
the plugs, even when the operator’s hands become benumbed by cold, or 
he has to wear gloves. 





















TESTING EQUIPMENT AND FAULT LOCATION 


271 


The coils in the bridge arms are also on the “plug-in” plan and by an 
arrangement shown in Fig. 333, any coil may be used in either bridge 
arm, thereby avoiding the use of a commutator and two extra plugs. 

The coils have one terminal connected to a central bar on the inside 
of the set, indicated by dotted lines, which forms a common centre; the 
other terminal is connected to the blocks between the parallel bars stamp¬ 
ed A and B. The terminal of the 1 ohm coil being connected to the block 
marked “10” and so on. It is thus evident that any coil can be placed in 
marked “1”, the terminal of the 10 ohms coil being connected to the block 
either bridge arm by simply plugging in the desired coil to the bar A or B 
as required. This arrangement also has the decided advantage that the 
formula for the unknown resistance is always X = A -f- B X R, be¬ 
cause the operation of transferring the plug from one side to the other 
does not interchange the bridge arms A and B in relation to the arms X 
and R, but only transfers a particular coil from one bridge arm to the 
other. 



Fig. 333. 

The Rheostat, (See Fig. 332) consists of four rows of coils or “de¬ 
cades” as each row is termed, and each row is divided into nine coils each 
of values 1, 10, 100, and 1000 ohms. As previously stated there is but 
one plug with its corresponding contact to each unit, ten, hundred or 
thousand numeral in the total. The decade arrangement is also conven¬ 
ient because it is formed of groups of coils in which each member of a 
group has a resistance which is the same as that of all the other members 
of the group. The facility with which a particular setting of the rheostat 
plugs may be read is very striking. 


/ (/; 

VVWWWW*— 4 * 
( 2 )” 3 

WVVWWNAA 

\AAAA/WVW 

VWVVVWVA*- 

{ 5 ) 


Fig. 334. 

Example —Referring to 332, the rheostat setting is bl92, which is 
very easily read from the position of the plugs. In the postofhce type it is 
necessary to go through a mental process of adding together odd values. 
The decade plan generally calls for a greater number of coils than the 
postoffice type since nine of the one ohm coils are requited in the units 















272 


TELEPHONOLOGY 


row, nine ten ohm coils in the tens row, and so on. The Leeds & Northrup 
Co., have, however, a scheme whereby but four coils are used in each row 
or decade. This is accomplished by a method of short circuiting certain 
coils, as explained by Fig. 334. Since the manipulation of the “decades” 
is just the same, as if nine coils were used in each, it is not essential, to 
understand the details of the method. Because of its novelty, however, an 
explanation is introduced for those who desire to become acquainted with 
it. 

Referring to Fig. 334, the resistance coils 1, 3, 3 1 and 2 ohms are 
connected in series as shown. 

Let the terminal of the 1 ohm coil and the 2 ohm coil and the points 
of union of the coils be numbered (1), (2), (3), (4), (5) as shown in 
Fig. 334. The current enters at point (1) and leaves the coils at the point 
(5), traversing 1, 3, 3 1 , 2=9 ohms in all. If this series is multiplied by 
any factor n then n (1 -j- 3 + 3 1 +2) = n 9 ohms. It will be seen that 
if the points (1) and (5) are connected all the coils are short circuited 
and that the current will traverse zero resistance. If the points (2) and 
(5) are connected the 3, 3 1 and 2 ohm coils will be short circuited and the 
current will traverse 1 ohm. By extending this process so that we con¬ 
nect two and only two points at a time, it is possible to obtain the regular 
succession o. values n (0, 1, 2, 3, 4, 5, 6, 7, 8, 9), the last value being ob¬ 
tained when no points are connected. The following table shows the 
points which must be connected to obtain each of the above values and the 
coils which will be in circuit for giving each value: 


Value. 

0 

1 

2 

3 

4 

5 

6 

7 
9 

8 


Points Connected. Coils Used. 


(5—1) 

0 

(2—5) 

1 

(4—1) 

2 

(2 4) 

1,2 

(3—5) 

1,3 

(1—3) 

3\2 

(2—3) 

1,S\2 

(5—4) 

1,3,3 1 

(0) 

l,3,3h2 

d—2) 

3,3\2 



Fig. 335 shows the method of connecting these points, two at a time, 
with the use of a single plug and corresponds to a row or “decade.” The 
circles in the diagram represent the brass blocks forming the plug holes, 
but for convenience of illustration they are shown, with a considerable 
distance between them. 











TESTING EQUIPMENT AND FAULT LOCATION 


273 


To the first two blocks at the top of the rows, the points 5 and 1 of 
Fig. 334 are connected, to the second two the points 2 and 5 are connected 
and so on, no points being connected at the last pair of blocks. It is evi¬ 
dent that if a plug be inserted between the blocks 1 and 5, the points 1 
and 5 of diagram are connected giving the value 0, if between the blocks 2 
and 5, the points 2 and 5 are connected giving the value 1 and so on. The 
value 9 is obtained when the plug is disposed of by being inserted in the 
last pair of blocks which have no connections. 

In the tens row it is understood that the values used are 10, 20, 30 
and 40 ohms, and so on, for the hundreds and thousands. 

Directions for Using the Decade Bridge, Shown in Fig. 332, for the 
Measurement of Resistances .—Referring to Fig. 332 the unknown resis¬ 
tance X, which is connected to the binding posts X, and X 2 is determined 
by the formula, X = A -r- B X R. Proceed as in using the postoffice 
lype of bridge excepting that the inserting of a plug gives a resistance 
value, and that but one plug is required for each row of resistances in the 
rheostat. The blocks marked R-V and R must have a plug inserted in 
them in order to have the bridge arrangement correct for resistance 
measurements. 

The best bridge values for various resistances are shown by the fol¬ 
lowing table: 

Unknown Resistance. Resistance plugged in bridge arms. 






A 

B 


Below 

.9999 

ohms 

1 

10000 

Divide by 10000 

.9999 

ohms 

to 

9.999 

1 

1000 

“ “ 1000 

9.999 

<< 

<i 

99.99 

10 

1000 

“ “ 100 

99.99 

u 

u 

999.9 

100 

1000 

“ “ 10 

999.9 

u 

a 

9999 

1000 

1000 

Even Ratio 

9999 

u 

a 

99990 

1000 

100 

Multiply by 10 

99990 

u 

u 

999900 

1000 

10 

“ 100 

999900 

a 

a 

9999000 

1000 

1 

“ 1000 

9999000 “ 

u 

99990000 

10000 

1 

“ 10000 


Dial Decade Testing Set .—In this form of Wheatstone Bridge, the 
resistances in the rheostat and bridge arms, are thrown in or out by the 
movement of a switch over contacts. In the usual form, the rheostat is 
made up of 10 one ohm coils, and 9 each of ten, one hundred and one thou¬ 
sand ohm coils, and values of one, ten, one hundred, and one thousand 
ohms, in each of the bridge arms. The use of dials has the advantage of 
quicker manipulation, especially when compared with the “postoffice” type 
of bridge. It is essential, however, that the mechanical construction of 
the switches be such, as to withstand long and continued use, without be¬ 
coming tight in their central bearings, or tending to cut the contact studs, 
over which they move. 

The dial testing set shown in Fig. 336, is manufactured by the Leeds 
& Northrup Company, and has embodied in it several important features, 
the most novel of which, is the arrangement of the bridge arms. In the 
usual form of the dial bridge, as above stated, each arm is controlled by 
a switch which has the objection of introducing a contact resistance di¬ 
rectly into the ratio coils. 

To overcome this, a scheme for connecting the ratio coils shown in 

Fig. 337 has been adopted. 

18 



274 


TELEPHONOLOGY 


It will be noted that from point X' to the point M or the ends of the 
two bridge arms, there are the seven resistances, a, b, c, d, e, f, g adjusted 
to a high degree of accuracy, and o p such values that when the switch S is 
set on any of the contacts, the ratio A B will be that marked for any 
particular setting. Therefore in resistance measurement, the rheostat set¬ 
ting is simply multiplied by the figure to which the Ratio arm points. 

The switch S is in the battery circuit and any resistance in its con¬ 
tact does not affect the accuracy of the ratio coils. 



DIAL DECADE TESTING SET. 

DIRECTIONS 


THE 1 ccris & NOR THRUP CO. MAKERS Phi^ a. 


Fig. 336. 


The manipulation of the bridge is very much simplified since any un¬ 
known resistance under measurement, is given by the setting o^ the rheo¬ 
stat for any particular balance, multiplied by the setting of the ratio or 
bridge arm switch S used in the measurement. If, S is set on 1, then the 
unknown resistance is the rheostat setting multiplied by 1, or it is read 
directly in terms of the rheostat. If as shown in the diagram S is set on 
10, then the unknown resistance is the rheostat setting multiplied by 10; 
if S is set on .1, then the unknown resistance is the rheostat setting multi¬ 
plied by .1 and so on; or if A = Ratio Dail Setting, R = Rheostat 
Reading, then X = AR. The complete connections for this instrument 
are indicated by Fig. 338. 

The rheostat consists of four dials or decades of 10 coils in the units, 
and nine coils each in the tens, hundreds, and thousands, making a total 




























TESTING EQUIPMENT AND FAULT LOCATION 275 

range of ten thousand ohms. The switch construction is such that the 
dials may be rotated continuously in either direction. This feature is 
very useful since it is an easy matter to turn from the highest unit in any 
particular dial to the lowest without the necessity of turn-back through 
all the other resistances as is the case in many forms of dials. This is ac¬ 
complished in the instrument illustrated by providing an inner contact 



ring. The contact brushes in their construction are made up of a number 
of separate leaves so as to insure good contact by each individual leaf 
making independent contact. The ends of the brushes are bent so they 
do not lie tangent to the circle in which they move, and consequently do 
not wear rings in the blocks. 



Fig. 338. 


The small knife switches are used to arrange the internal connec¬ 
tions of the bridge for the various tests that can be made with this instru¬ 
ment, viz., measurement of resistances, location of faults, crosses, and 
grounds by the Murray and Varley Loop methods, locations of opens, and 

















































276 


TELEPHONOLOGY 


insulation measurements. The last named test should be made with the 
instruments described under Cable Testing Apparatus, where accuracy is 
required. 

The galvanometer is of the D’Arsonval type and the set also contains 
batteries with necessary keys, forming a complete unit. 

Slide Wire Bridge .—The slide wire form of Wheatstone Bridge is the 
same in theory as the postoffice or decade type, but differs in the use of a 
straight wire for the bridge arms. The bridge arms are variable and the 
rheostat is a fixed value, and it, therefore, differs in these respects from 
the bridges described heretofore. The scale of the bridge wire can be 
calibrated so as to read directly in ohms resistance, and it is then called 
an OHMMETER. 



Fig. 339. 


Reference to Fig. 339, will show it to have the theoretical connections 
of the Wheatstone Bridge. 

The movable contact P forms the junction point of the bridge arm A 
and bridge arm B for any particular balance of the bridge. The wire 
from 1 to 3 is usually divided into 1000 parts and if the wire is uniform 
in cross section, it will then have a resistance directly proportional to its 
length, so that the number of divisions between 2 and 3 can, therefore, 
represent the value of the bridge arm A, and the number of divisions be¬ 
tween 2 and 1, the value of the bridge arm B, without referring directly 
to their resistance in ohms. This is true since the value of the unknown 
resistance is determined in terms of the rheostat by the ratio of the 
bridge arms to each other, so consequently, it is immaterial whether we 
express the ratio in ohms or in length of wire. 

If the contact P is at 700, then the bridge arm A will have 700 parts 
in it, and the arm B will have 1000 parts—A or 300 parts in it. There¬ 
fore the ratio 

A A 


B 1000—A 

and the formula for the unknown resistance becomes 

A 

X = - R 


1000—A 









TESTING EQUIPMENT AND FAULT LOCATION 277 

The bridge wire, in order to be sufficiently long, so as to give accur¬ 
acy of setting, is usually made one meter. This length of wire would 
make a portable instrument too bulky, and consequently, it is customary 
to use a number of shorter lengths joined in series, but having a total 
length of one meter. 



Fig. 340. 

A slide wire bridge is illustrated in Fig. 340 and Fig. 341. It will be 
noted that the bridge wires are joined by terminating in heavy blocks so 
as not to introduce any extra resistance into the slide wire circuit. 

The ratio coils are so arranged that any one of the four values indi¬ 
cated, may be connected in the rheostat arms. The pointer or stylus for 
moving along the slide wire usually consists of a conveniently arranged 
touching device with a hard rubber insulating handle. 



The method of operation is to connect the unknown resistance to be 
measured in the posts provided for the purpose, and touch the various 
wires until a balance is obtained. The instrument illustrated is arranged 







































278 


TELEPHONOLOGY 


for a telephone instead of a galvanometer, but a galvanometer can be sub¬ 
stituted by connecting it in the same posts. 

If the instrument is a Direct Reading Ohmmeter, the wires will have 
four sets of scale values, one to correspond with each value of the ratio 
coil. 

Lineman’s Fault Finder .—This instrument is a Wheatstone Bridge 
of the “slide wire” type, but has several advantages as compared with the 
slide wire instrument shown in Fig. 340. In all bridges having stretched 
wires, in order to secure a high resistance, it is necessary to use fine 
wires, and this is open to the objection that such wires are not mechani¬ 
cally strong. Another disadvantage of the general form is the use of the 
hand stylus on the wires. These objections have been overcome in the 
Lineman’s Fault Finder, shown in Fig. 342, by winding the bridge wire 
helically, insulating the adjacent turns, and then placing the entire wind- 



Fig. 342. 


ing on the neriphery of a disc, about six inches in diameter. The wire is 
on the inside of the case. The contact is of the brush form, and is operat¬ 
ed by means of the hard rubber head in the centre of the scale plate. The 
scale is divided into 1000 parts, and attached to the head operating the 
slide contact is an index. This instrument is arranged for the measure¬ 
ment of resistances and the location of faults, crosses, and grounds by the 
Murray & Varley loop methods. It can also be used for the location of 
opens, in which case a telephone and source of alternating current is used 
instead of the contained galvanometer and battery. These two acces¬ 
sories, the latter in the form of a little buzzer or “tone test,” are always 
to be found in a telephone equipment. 






























TESTING EQUIPMENT AND FAULT LOCATION 


279 


The complete connections and diagrams for each test, with diagrams 
for operating, will be found fully described on page 

This instrument is complete with a sensitive D’Arsonval Galvano¬ 
meter and Battery. The small knife switches are used to arrange the 
bridge connections, so as to simplify the manipulation of the outfit. The 
battery circuit is closed by depressing the rubber head controlling the 
contact on the slide wire, and the galvanometer is also provided with a 
special key. 

The simplicity of design combined with the fact that the results are 
obtained with very little calculation makes this instrument an ideal one 
to place in the hands of Cable Splicers and Inspectors. Since the expen¬ 
ses connected with the maintenance and repairs of telephone lines and 
cables are a very considerable part of the operating expenses of a tele¬ 
phone company, any apparatus which simplifies the locating of trouble 
is of decided importance. The reader is referred to the section on fault 
location for a complete set of diagrams and working formulae for use 
with this instrument. 



Fig. 343. 


Cable Testinn Sets .—The term “Cable Testing Set” is applied to an 
outfit made up of one or more units, and is more extended in its range 
than the instruments described under “Portable Testing Sets.” They 
generally include the features of an ordinary bridge set, although if ar¬ 
ranged only for the measurements of insulation and capacity, the same 
outfit can not be used or fault location. The measurements with such 
outfits can be made to a higher degree of accuracy, due primarily to the 
use of a sensitive reflecting galvanometer, and the fact that all parts are 
highly insulated from each other, as compared with the testing sets de¬ 
scribed heretofore. 

A number of type forms will be described. 









280 


TELEPHONOLOGY 


Fisher Portable Cable Testing Set No. 1.—This instrument is shown 
in Fig. 343 and represents the highest development in this class of appara¬ 
tus. its design, this set gives the maximum of simplicity, accuracy and 
convenience of manipulation. The most distinguishing feature of the 
the instrument is the MASTER SWITCH by means of which, the connec¬ 
tions can be made for the various tests by a single movement, thus avoid¬ 
ing the labor and time which have to be expended in interchanging the 
connections and memorizing the rather complicated scheme of connections. 

In range, this set can be used for the measurements of capacity, insu¬ 
lation resistance, conductor resistance, and the location of faults, crosses, 
and grounds by the Murray & Varley loop methods. 

The following parts are included in the set, as shown in Fig. 344, 
Decade Wheatstone Bridge, Battery, Galvanometer, Ayrton Shunt, Stand¬ 
ard Sub-divided 1-2 Micro-farad Condenser, Standard 1-10 Megohm, Bat¬ 
tery and Galvanometer Reversers, necessary Keys for charging, discharg¬ 
ing and short circuiting, and MASTER SWITCH. 



The Master Switch, which is a distinguishing feature of this set, and 
which has been referred to, is illustrated by Fig. 345 and 345a. 

When the pointer indicates “Bridge” (See Fig. 344) the two ad¬ 
jacent jaw contacts are connected, Fig. 345a and in the same manner the 
corresponding jaw contacts which are beneath these two, as indicated in 
Fig. 345, are connected. The connections from the jaws go to the differ¬ 
ent parts of the instrument required for the particular test as shown by 
the index. Thus when making a measurement it is only necessary to ro¬ 
tate the switch so that test and all connections are automatically made. 

The connections in the switch are of the knife and jaw type and are 
thoroughly reliable. The Master Switch can readily be taken apart for 
cleaning or inspection. 

In making measurements of insulation or capacity, all parts involved 
in the test must be highly insulated so as to reduce to a minimum any 
leakage between the parts giving a false deflection on the galvano- 





















































TESTING EQUIPMENT AND FAULT LOCATION 


281 


meter. This is especially true when a set is to be used out-of- doors and 
frequently in damp places. To avoid this difficulty, the posts which re¬ 
quire such protection, are mounted upon hard rubber pillars, with a “pet¬ 
ticoat” or groove to increase the leakage surface. A section of one of 
these is shown in Fig. 346, from which it will be noted that ample insula¬ 
tion surface is provided both above and below the main hard rubber plate. 
When placed directly on the ground the set as a whole is insulated by 
means of four rubber insulators, which are mounted on the inside of the 
lid when not in use. The illustration in Fig. 347 shows the set mounted in 
this manner. 

The connections between the different instruments composing the set 
are made in all cases by means of heavy bare copper wires which are run 
through the air from the brass rods projecting through the insulating pil¬ 
lars. The connecting wires are securely fastened by binding against the 
brass rods with small copper wire, and soldering. They are run at such a 
distance from each other that there is no danger of their touching. In 
this way three very important points are secured. The insulation is very 
high and will not degenerate, as might happen if covered wires were de¬ 
pended on. All of the connections are very easily inspected and thorough¬ 
ly reliable contacts are insured. 



Fig. 345. 



Fig. 345a. 


The galvanometer shown in Fig. 348 is a sensitive reflecting D’Ar- 
sonval arranged for cable testing and mounted upon a street tripod. The 
galvanometer can be placed in its carrying case and the tripod folds up 
as shown in Fig. 349. The Cable Testing Set and Galvanometer case are 
shown with canvas carrying cases around them for protection. 

A brief description of the component parts of the Fisher No. 1 Set 
will be given: 

Wheatstone Bridge is of the plug decade type and is the same as de¬ 
scribed on page 

The Shunt is of the Ayrton Universal type, and hence can be used 
with galvanometers of any resistance. In addition to general practice it 














































282 


TELEPHONOLOGY 


is provided with a 1-10000 shunt, and therefore under ordinary conditions 
can be used with very sensitive galvanometers where the insulation con¬ 
stant of the galvanometer may be several hundred thousand megohms 
with 100 volts. 

The Standard 1-10 Megohm is made of two coils of 30,000 and 70,000 
ohms respectively, and is provided with plugs by which one or both can 
be cut out. It is also provided with binding posts at each end, so that if 
necessary it can be used apart from the set. 



Fig. 346. 



Fig. 347. 


The Standard Condenser is sub-divided into 5 sections of 1-10 M. F. 
each. The sections are connected between parallel brass blocks so that by 
simple combinations all values from 1-10 up to 5-10 M. F. can be gotten. 

The Battery is 10 cells of a type of semi-dry cell which has an E. M. 
F. of about 1.5 volts per cell when new. It is connected to the Battery 
posts by means of flexible leading wires. 

The Battery and Galvanometer Reversers are the double-throw, 
double pole type of switches, and with this style of switch there can be 
no possible question of a bad contact, which is often the case with some 
types of reversing switches. They serve both as reversers and as a 
means of breaking the circuit to which they are attached. 

The Keys are arranged so as to perform the necessary functions for 
the various tests. The short circuit key is arranged so that it can be in¬ 
stantly changed from a permanent to a tapping short circuit. By press¬ 
ing down the button A (Fig. 344) a permanent short circuit is made 
through a knife and jaw. B is attached to a strip of spring brass, under¬ 
neath which is a rigid arm. When B is depressed, it first bends the 
spring, then coming in contact with the rigid arm opens the circuit at A 
and immediately afterward makes it at B by bringing two contacts to¬ 
gether. This contact opens as soon as the spring is released and forms 
the tapping short circuit. 

The Contained Galvanometer is a D’Arsonval and of ample sensibility 
for all measurements of resistance and fault locations unless the latter are 
extremely high. 




















TESTING EQUIPMENT AND FAULT LOCATION 


283 


The External Galvanometer, Fig. 348, is a reflecting D’Arsonval and 
has in its design certain features which make it easy to set up and operate 
as compared with the usual laboratory form of instrument. The moving 
system is visible through a glass window and there is ample clearance be¬ 
tween the coil and the core. An index is provided on the coil and core so 
that it is an easy matter to tell when the coil is swinging centrally in its 
field. The reading telescope is of a special design of unusually high mag¬ 
nifying power. Although the telescope arm is only 15" long and the scale 
8" long, the magnifying power is such that the appearance is the 
same as that of a scale at a meter’s distance viewed with an ordinary tele¬ 
scope. The scale has 250 divisions each side of the zero. 



Fig. 349. 



This optical system is one which makes it particularly easy, to find 
the scale,” and in setting the instrument up no delay is occasioned in 
getting it properly adjusted and focused. The galvanometer is clamped 
on the head of the tripod by two wing nuts. To remove the instrument 
it is only necessary to unscrew these a few turns and swing them out. 





284 


TELEPHONOLOGY 


The Fisher Portable Cable Testing Set No. 2.—The requirements for 
a cable testing set can often be met by an outfit which has its parts sim¬ 
plified as compared with the Fisher No. 1 Set, and when the conditions, 
under which it is to be used, will not require extremely high insulation. 
These limitations will permit the design of an outfit which is lighter, and 
consequently, such an outfit will be more portable. 

The Fisher Portable Cable Testing Set No. 2 has the same range and 
accuracy as the Fisher No. 1 Set, but the parts are not as highly insulat¬ 
ed. Its insulation is such, however, as to be found entirely satisfactory, 
except under the most trying conditions of moisture. 

In range, this set can be used for the measurements of electrosta¬ 
tic capacity, insulation resistance, conductor resistance, liquid resistance, 
the location of faults, crosses, and grounds, by the Murray and Varley 
Loop Methods, and locating breaks in cables. 



Fig. 350. 


This instrument is illustrated by Fig. 350 and Fig. 351. In consists 
of a modified form of Wheatstone Bridge, rheostat, battery, galvanomet¬ 
er, Ayrton shunt, standard condenser, standard 1-10 megohm, keys, com¬ 
mutator for producing an alternating current, and switches for quickly 
making changes from one test to another. 

The Wheatsone Bridge adopted in this set is a marked variation 
from the bridges described thus far and is a type known as the Kelvin- 
Varley Slides. It is a form having the bridge arms variable and the rheo¬ 
stat fixed, as in the slide wire bridge, but the resistances in the bridge 
arms are made up of resistances in the form of coils. This arrangement 
gives the slide wire a much higher resistance, and by means of a system 
of shunting, the coils comprising the bridge wires, can be read to their 
thousandth part. 

The arrangement of the bridge arms is shown in Fig. 352. The 
points marked G and B are the points of attachment for the galvanometer 
and battery. At R are represented the four coils of the rheostat, any one 
of which may be used, and at X, the unknown resistance. Between M and 
N are eleven coils of equal value which form the bridge wire. There is a 
contact point between each coil and the one next to it. The other coils 
shown in the series marked “Tens” “Units” are used to sub-divide the 
coils of the bridge. They constitute what may be .called an electrical ver- 















TESTING EQUIPMENT AND FAULT LOCATION 


285 


nier, by means of which the bridge wire is sub-divided to thousandths of 
its total value. The two arrows in contact with the points marked 1 and 
3 in the “Hundreds” row and with the 2 and 4 in the “Tens” row repre¬ 
sent contact arms which can be moved along to make contact at any of the 
contact points, but are always at the same distance apart so that they have 
two coils between them. They are connected to the ends of the row of 
coils below them so that these two coils are shunted with the entire row 
of coils below. Consider now the result of this shunting in the case of the 
“Tens” and Units” coils. The tens are, for example, eleven coils of 80 
ohms each. The units are ten coils of 16 ohms each. The two 80 ohm 
coils between the points 2 and 4 are shunted with the ten 16 ohm coils; 
160 ohms is shunted with 160 ohms, and the resistance between the points 
2 and 4 becomes 80 instead of 160 ohms. There are then in the “Tens” 



series, for any position of the double arms, actually ten resistances of 80 
ohms each. The point of the Battery contact may be placed at any posi¬ 
tion in the “Units” series, thus sub-dividing the shunted coils in t he 
“Tens” series to tenths. The coils in the Hundreths” series are 400 ohms 
each, and are sub-divided in the same way by those in the “Tens” series. 
An example will make the use of the bridge clear. Assume that a balance 
is obtained with 100 unplugged in the rheostat and the contacts in the 
position shown. The bridge reading is then 237. Call this value A. Then 

A 237 

X* R:: A: 1000—A, and X = R -- = 100 — = 31.06 

1000—A 763 


The calculation of the fraction 

237 


763 
















































































286 


TELEPHONOLOGY 


would take considerable time and might lead to errors. To overcome the 
necessity for this is furnished conveniently fastened into the lid of each 
set, a table giving the values of 


1000—A 


A 

for all values of A between 0 and 1000. Reference to the table show’s 


A 

- = .3106 for A = 237. 

1000—A 


We have, consequently, simply to multiply the value taken from the 
table by the resistance unplugged in the rheostat to determine the value 
of X. From this it will be seen the Wheatstone Bridge measurements 
may be made and calculated very rapidly. 

In the actual construction the coils are arranged in three dials as 
shown in Fig. 351. 



HUNDREDS 


UNITS 

B 

Fig. 352. 


The Testing Set shown in Fig. 353, differs from the Cable Testing 
Sets described thus far in that the parts are made up of separate units 
instead of being combined and permanently connected. It is useful when 
accurate measurements of insulation and capacity only are to be made, 
and finds application by construction companies who wish to make an in¬ 
sulation test on a newly constructed telephone line before turning the line 
over. 

The Set consists of a sensitive reflecting D’Arsonval galvanometer, 
complete with street tripod and repair kit, Ayrton Shunt, 1-10 Megohm 
Standard Resistance, and a Standard .3 M. F. Condenser, complete 
with charge and discharge key. The last named parts mounted in hard 
rubber cases so that in manipulating them, they may be held in the hand 
without interference of leakage from the operator to ground. 

Insulation Measurements are to be made with the apparatus as 
shown in the diagram, Fig. 354. 

In general, the usual direct deflection method is used. The constant 
of the galvanometer is determined by observing the deflection due to the 







TESTING EQUIPMENT AND FAULT LOCATION 


287 


current from a definite battery through a known resistance (100,000 
ohms), the galvanometer being shunted. The deflection of the galvano¬ 
meter due to the current from the same battery through the insulation re¬ 
sistance to be measured is observed, and from these two deflections the 
insulation is calculated. 

The apparatus and arrangement differ from that usually employed. 
1st. In that the battery key is combined with the shunt. 2nd. In that 
there is no short-circuit key for the galvanometer. 

The battery key b is combined with the Ayrton Shunt for compact¬ 
ness and also for convenience in manipulation. The knob a controls the 
key b and is mounted so that it projects up through the handle which ope¬ 
rates the shunt. By depresssing a, the contact b is closed. This is ar¬ 
ranged so that it can be locked in the closed position. 



Fig. 353. 


The galvanometer short-circuit key is omitted partly in the interest 
of simplicity of working and compactness and primarily to avoid the bad 
effects due to using a short-circuit key with a damped D’Arsonval Gal¬ 
vanometer. As is well known, a D Arsonval Galvanometer damped to 






















288 


TELEPHONOLOGY 


give a satisfactory period of deflection becomes exceedingly unsatisfac¬ 
tory and sluggish when it is short-circuited. The necessity for using a 
short-circuit key is avoided by connecting the shunt as shown in the dia¬ 
gram. With the shunt switch on the position zero, the galvanometer is 
out of the circuit and no current passes through it. The battery key being 
closed, the course of the current is from one side of the battery through 
the insulation of the cable (or the 100,000 ohm box as the case may be) to 
Ga. through a and b, to the other side of the battery. This is the position 
used during the period of electrification of the cable. 



Fig. 354. 


This arrangement has the additional advantage of protecting the 
galvanometer against excessive deflection when a leaky cable is under in¬ 
vestigation. The galvanometer deflection is taken by moving the shunt 
from the position zero toward the position 1, and in the case of a leaky 
cable, there would be small deflection with the shunt on the position .0001 
or .001, and the excessive deflection which the unshunted galvanometer 
would get could be avoided. 

The shunt may be held in one hand while its handle and the knob a 
are manipulated in the other. This is the customary method of working. 
In order to make it entirely free from leakage, the shunt is mounted in a 
hard rubber case. 

The 100,000 ohm box is arranged without any provision for short- 
circuiting the resistance. This is done because in the great majority of 
cases, it is not necessary to make any correction for the addition of 100,- 
000 ohms to the insulation under measurement. In a few cases where the 
correction is necessary, it can be made, or the two binding posts can be 
connected by a piece of wire to cut out the resistance. 











TESTING EQUIPMENT AND FAULT LOCATION 


289 


The simplicity of the arrangement and its operation will be made en¬ 
tirely clear from the following directions for making measurements. 

Directions for Insulation Measurements .—Connect a suitable battery 
(100 cells) as shown in the diagram drawing, connecting one terminal of 
the battery directly to the 100,000 ohm box instead of to the cable. Close 
battery key b by depressing a and move the shunt to the position .0001. 
With 100 cells of battery, the galvanometer will now give a readable de¬ 
flection. Call this deflection D' and the shunt position S', then the insula¬ 
tion constant of the galvanometer in megohms will be 


D' 


10xS' 

For instance, if D' = 80 and S' as above = .0001, then 

80 

Const. = - = 80,000 megohms. 

10X.0001 

To determine the insulation of the cable, reset the shunt at the posi¬ 
tion zero and connect in the cable as shown in the diagram. Close the bat¬ 
tery key b and after allowing a sufficient period for electrification to 
elapse, move the shunt successively over the position .0001, .001, .01. 1, to 1, 
observing the galvanometer to see that it does not give too large a deflec¬ 
tion. When a readable deflection is gotten, note it and the shunt position. 
Call this deflection D and the shunt position S, the insulation I to be de¬ 
termined will then be 


Const. X S 

I = - 

D 

If, for example, the deflection D is 40 and the shunt position S is I, 
the constant as above determined being 80,000, then 

80,000 

I = - = 2,000 megohms. 

40 

Measurement of Capacity. —For this purpose a one-third micro-farad 
standard condenser and condenser switch are used. The construction o± 
this and the method of operating it are clearly shown in the diagram. The 
case is made entirely of hard rubber and the parts are very well insulated 
so it may be held in the hand without danger of error while making a 
test. 

The method is the usual one of comparing the discharge from the 
cable with that from the standard condenser. Although the galvano¬ 
meter is damped the deflections are strictly proportional to the capacities. 
With a plug in the position “Cab,” the deflection due to the cable can be 
taken, and with it in the position “.3 M. F.”, that due to the standard 
condenser can be taken. See Fig. 355. 

19 






290 


TELEPHONOLOGY 


The Location of Faults. 

One of the most common and at times, one of the most difficult tests 
to make, requiring skill and judgment in testing is the location of a 
“fault.” The term “Fault Location” is understood to mean the location 
of a cross, ground or other similar disturbing influences, which have in¬ 
terrupted perfect service upon a line. The location of “opens” or com¬ 
plete break is usually considered as distinct from ordinary ground and 
cross location, although in making such a determination the bridge is 
used in a manner similar to some forms of fault location. 



The fundamental principles in fault location are quite simple but in 
many faults, we have to deal with conditions which are variable and often 
undeterminable, so that the location of a fault is not always reduced to 
the SIMPLICITY OF SUBSTITUTING QUANTITIES IN A FORMULA. 
This foregoing statement is made, so as not to mask a well known 
truth among experienced testers, but it is not to be inferred that all fault 
location must necessarily be a complex measurement. The use of a bridge 
on line trouble will soon give an inexperienced operator confidence, which 
in conjunction with a close study of the line conditions, will place him in 
a position to locate faults with rapidity and accuracy. 

The subject of localizing faults has been given considerable study and 
many specialized methods have been adopted. The conditions to be met 
and cautions to be observed when locating a fault in a submarine cable 
are quite different from those encountered in land lines. The same ap¬ 
plies when locating faults in low resistance conductors, such as power- 
feeder cables, as compared with the higher resistance telephone circuits. 

To give a critical discussion for each case that might arise, is beyond 
the scope of this article, but the fundamental principles will be shown and 
attention will be called to some general facts relating to fault location. 

The more common methods of locating a fault are by means of the 
Murray and Varley Loop. The fundamentals of both methods are quite 
simple but, as will be shown later, each one has special applications. 

In making either of the loop tests, it is necessary to have a complete 
circuit, from one binding post of the instrument, through the fault sec¬ 
tion, and back to the other binding post. The circuit is called the “loop.” 








































TESTING EQUIPMENT AND FAULT LOCATION 291 

Theory of the Murray Loop .—As already explained, a bridge is bal¬ 
anced when the arms of the bridge shown in Fig. 356, when A: X :: B 
: R or 


A B 

X R 

and we shall now see that in loop testing, we make use of this bridge ar¬ 
rangement. 

In the Murray Loop Test, shown diagrammatically in Fig. 357, the 
two ends of a loop which has a fault at F are connected to the two arms 
of a bridge at C and E. It is thus evident that the resistance of the circuit 
from C to the fault F and from the fault F to E form two arms of the 
bridge, with b and d as completing arms. The battery connection is 
grounded at the instrument and flows through the earth to the fault F. 
The galvanometer is connected as shown. 




When the bridge is balanced b Y = d X 

Let L be the total resistance of the loop from C to E. 

Then X + Y = L 
Therefore Y = L — X 

Substituting this value of Y in the above equation, 

b(L — X) = d X 

L b 

From which X = - 

b + d 

The above simple algebraic solution for the fault will be sufficient to 
show the fundamentals of the Murray Loop Test, and some consideration 
will now be given to the “practice” of fault location. 

The result for X is in ohms, but knowing the size of the conductor, 
its resistance per unit length can be obtained from any wire table or it 
can be obtained directly from the formula as will be shown later. 

It will be noted that the loop measurement made, is independent of 
the resistance of the fault, for, just as in the Wheatstone Bridge circuit, 
any resistances in the battery and galvanometer circuit do not affect the 
ratio of the bridge arms. When the fault has a high resistance, then but 
little current can flow, and in order, therefore, to increase the sensibility 
of the galvanometer it becomes necessary to add more battery. If the 

















292 


TELEPHONOLOGY 


fault in a grounded or crossed conductor were always of negligible resis- 
tance, in other words if it were a “dead” short circuit or ground, its loca¬ 
tion could easily be detected by measuring the resistance from the point 
of test and back again through the ground or through the other conductor 
affected in case of a cross. This, however, is very seldom the case and it 
becomes necessary to employ tests, such as the loop, giving results inde¬ 
pendent of these resistances. 

Murray Loop With Post Office Bridge .—The foregoing remarks will 
enable the reader to understand the use of the postoffice bridge, which has 
already been described for the measurement of resistances and the test¬ 
ing sets to be described later, for the location of a fault by the Murray 
Loop Method. The bridge is shown in plan in Fig. 358 and the theoreti¬ 
cal diagram, Fig. 359, indicates the connections when the instructions 
given are followed. It will be noted that the rheostat of the bridge is the 
only adjustable arm but so long as we maintain the quality required by 
the law of the bridge, we can divide any one of the four arms into fixed 
and adjustable arms. 



Join the faulty and good wires at the distant end of the cable; con¬ 
nect the faulty conductor to X 2 and the good wire to Measure the to¬ 
tal resistance of the loop and call this r. The connections for making the 
resistance test are the same as described under “Resistance Measure¬ 
ments.” Plug R 2 to block G, disconnect R 2 from Ba 1 , and connect Ba l to 
ground, or if the fault is a cross, connect Ba 1 to the wire crossed with the 
faulty wire. Connect B to R and A to X, plug in all the coils in arm B and 
unplug 1000 ohm coil in arm A. Then vary the rheostat until a balance 
is obtained. 

Letting r = total resistance of loop, 
a = resistance to fault, 

A = resistance unplugged in bridge arm A. 

R = resistance unplugged in rheostat. 

Then, 

R r 

a = - = resistance to fault from post X„. 

A + R 




























TESTING EQUIPMENT AND FAULT LOCATION 293 

The result obtained thus far is in ohms but the distance to the fault 
can be expressed in feet by letting L = length of one of the two cables 
which are assumed equal, since a, the resistance to the fault, and r, the 
total resistance of the loop are proportional to the lengths, therefore, d, 
the distance to the fault is: 

2 L R 

d = —- 

A -f- R 



Example—The total resistance of a loop, one wire of which was 
faulty, was found to be 290 ohms. With 1000 unplugged in bridge arm 
A, a balance was obtained with 208.3 unplugged in the rheostat. 

Therefore, the resistance to the fault is 

208.3 X 290 

- — 49.993 ohms. 

1000 Ar 208.3 

Theory of the Varley Loop. —In this, as in the Murray test, the two 
ends of the faulty conductor must be accessible by forming a loop with it 
and a good return conductor. The connections are indicated in Fig. 360. 



It will be noted that in this test an adjustable resistance d (which is 
the rheostat of the bridge) is added in series to the faulty wire, and as 




























294 


TELEPHONOLOGY 


may be expected, the law of the Wheatstone Bridge is again applied. The 
loop C to E contains a fault at f, and if X and Y are the resistances to the 
fault from E and C respectively, then 

a(d + X) = bY, 

And, Y = L — X, 

Therefore, a(d -}- X) = b(L — X) j 


From which, 

bL — ad 

. X = - 

b + a 

If b = a then, 

L — d 

X = - 

2 

It is necessary that the faulty one of the two looped conductors be at¬ 
tached to E or the arm, having the adjustable resistance. If this is not 
done, after joining up it would be found that no balance could be obtain¬ 
ed, then we may be sure that the fault lies nearer C and E. 



Varley Loop With Post Office Bridge .—Join the faulty and good 
wires at distant end of cable and connect faulty to X 2 and good 
to X,. Measure total resistance of loop. Connect R 1 to G and Ba 1 to 
ground, or, if the fault is a cross, connect Ba 1 to the wire crossed with 
the faulty wire. Connect A to X and B to R, vary resistance in bridge 
arms and rheostat until a balance is obtained. 

The diagram of connections in Fig. 361 shows the relation of the bridge 
parts. 


r = total resistance of loop, 
a = resistance to fault, 

A = resistance unplugged in Bridge Arm A, 
B = resistance unplugged in Bridge Arm B. 
R = resistance unplugged in Rheostat. 




















TESTING EQUIPMENT AND FAULT LOCATION 


295 


Br — AR 

Then a = - 

A + B 

Example.—The total resistance of a loop, one wire of which was 
faulty, was found to be 290 ohms. With 10 unplugged in bridge arm A 
and 100 in bridge arm B, a balance was obtained with 2350 unplugged in 
the rheostat. 

Therefore, the resistance to the fault: 

100 X 290 — 10 X 2350 
- = 50 ohms. 

10 + 100 

General Remarks on Fault Location. —Having thus seen the applica¬ 
tion, of the loop test for the location of a fault, there are certain general 
facts which must be given consideration. 

It is a careful study of these various conditions which will often ex¬ 
plain the causes for apparent inconsistencies between results and calcula¬ 
tions. The “art” of locating faults is one based primarily upon practice, 
and the wire chief, who has not the ambition to take a portable testing set 
and “venture” cannot possibly hope to cope with conditions which are of¬ 
ten puzzling and hard to account for. 

The first great essential is to be sure, that the various connections 
are correctly made, and the contacts electrically perfect. If one has to rely 
upon an unexperienced assistant for making joints and connections on 
poles or elsewhere, much annoyance may be experienced. Too much em¬ 
phasis can not be placed upon the making of reliable connections, as any 
resistance caused by poor contacts, in the loop circuit will enter directly 
as an error in the location. If, for instance, the assistant in going to the 
end of the loop, did not join the faulty and good wire in a substantial 
manner, but had introduced a joint having a resistance of *4 W, and the 
loop consisted of No. 2. B. & S. Copper Conductor, then the location would 
be in error about 16 feet. Experience will teach one, however, to fre¬ 
quently detect improper and poor connections by the use of check meth¬ 
ods, or by duplicating some of the tests, or by special tests which one has 
learned to employ. 

Use Mate for Good Return. —In any case of cable trouble, if the mate 
of the faulty wire is good, always use it as the location will be much more 
accurate. When the good and bad wires are of different pairs, one may 
be longer than the other, thereby making a slight error in the distance to 
the fault. 

Loop May Consist of Different Sized Conductors. —If the loop is 
made up of several lengths of conductors of different sectional areas, as 
often occurs when cable circuits are joined to toll circuits, the distance to 
the fault is easily calculated, by expressing the different cross sections in 
terms of equivalent length of one of the conductors in the loop. To make 
this allowance, the cross sections and the lengths of the different sections 
must be known and should be reduced to the size of one of the conductors, 
by multiplying the length of each conductor respectively, by its rated re¬ 
sistance per 1000 feet and dividing the product by the rated resistance 
per 1000 feet of the size of the conductor to which it is being reduced. 





296 


TELEPHONOLOGY 


The following example will explain the process. In the loop shown in 
Fig. 362, the conductor in the cable section E consists of 2200 feet of No. 
19 B. & S., the conductor in the cable section F of 1400 feet of No. 22 B. 
& S., and the last section G is part of a toll circuit, consisting of 2160ft. 
No. 12 B. & S. 

To reduce the No. 19 and No. 12 in terms of No. 22, we have 

2200 X 8 038 

- = 1097 ft. of No. 22 is equal in resistance to 2200 ft. 

16.12 

of No. 19. 

2160 X 1.586 

- = 212.5 ft. of No. 22 is equal in resistance to 2160 ft. 

16.12 

of No. 12. 

This makes the total resistance of the loop equivalent to 1097 ft. 
1400 ft. + 212.5 ft. = 2709.5 ft. of No. 22 B. & S. conductor. If the result 
showed the fault, f is a distance of 1346 equivalent feet from A, of this 
1097 feet are in the section E. Consequently, the fault is 1346 — 1097 = 
249 feet from A. 

It is a practice in some cases, where two different sized cables are 
spliced, to mark on the cable diagram an extra scale for use in fault loca¬ 
tion. If for instance, the two cables spliced were Nos. 19 and 22, then for 
the lengths of the No. 19 cable, no extra scale or dimensions would be ad¬ 
ded, but for the No. 22, an extra fault location scale or dimension would 
be added. This scale would be double the actual cable lengths, since the 
No. 22 conductor has twice the resistance of No. 19 conductor. These dis¬ 
tances, given by the fault location scale, are used directly in the formula 
for fault location and the distance to the fault is read off on the fault lo¬ 
cation scale. 

Cable Inspection .—No matter how carefully the cable has been in¬ 
stalled, whether it be underground or overhead, too much emphasis can¬ 
not be laid upon its being tested and inspected so as to maintain the entire 
system at its maximum efficiency. The inspection should be done at regu¬ 
lar intervals, and attention given to the manholes, covers, protectors, ter¬ 
minals, hangers, junction boxes, etc. 

The cables are subject at all times to lightning, electrolysis, chemical 
action, heat, long continued vibrations, and mechanical injuries, so that 
the tester must ever be on the alert. 

Difficulties in Making Measurements .—Accurate measurements are 
often prevented by the influence of foreign currents, flowing in the loop 
or to neighboring circuits carrying heavy currents. If the galvanometer 
is of the magnetic or Thompson type, any surrounding magnetic distur¬ 
bances will cause it to show a “restlessness” but since modern testing sets 
are all equipped with D’Arsonval Galvanometers, which are not affected 
by neighboring magnetic fields, no further reference will be made to the 
former type. 

If due to foreign currents flowing in the loop, the Galvanometer 
will deflect as soon as the galvanometer Key is closed. This trouble is 




TESTING EQUIPMENT AND FAULT LOCATION 


297 


sometimes caused by ringing current flowing in and out, of a fault due to 
the capacity of the conductor or loop under test. Sometimes the testman 
can remove this by opening up a ringing generator wire, used through 
the cable to supply branch exchanges, with ringing current. If the testman 
cannot remove the disturbing current by shutting it off, he had better try 
another loop, or try the same one sometime later. 

Induced currents can be set up in a loop by a Morse line operating 
through the same cable, or by an outside power wire used for a good 
wire. It often becomes necessary to make use of another loop which may 
not be so bad. 

A disappearing ground is often encountered while trying to locate a 
fault. This is generally caused by the battery current from the testing 
set turning a slight moisture ground into gas. Sometimes by waiting for 
a short time the ground will reappear. By employing more battery so as 
to get a higher voltage, and taking a quick reading, it is sometimes possi¬ 
ble to catch a location. Sometimes the ground can be increased or perma¬ 
nently burned out, by applying ringing generator to the faulty wire. If 
these methods are not successful it is best to leave the trouble until it be¬ 
comes worse. A ground that is sufficient to make a line noisy can, as a 
rule, be located. 

Locating Grounded and Crossed Wires.—Preliminary Test. —The 
first step in fault testing is to ascertain the nature of the fault, by making 
a preliminary test of the reported trouble. This can be done from the ex¬ 
change end of the cable. The exchange end of the line should be cut off 
and the test made directly on the cable conductor terminals. The test con¬ 
sists of determining the electrical condition of the available wires. After 
making the preliminary test, the plan of the cable should be examined to 
see if it can be located in a particular branch or terminal by the readings 
obtained. 

Continuity. —To test for broken wires, the conductors should all be 
grounded at one end of the cable, and the test applied at the other end in 
the following manner: 

Ground one side of a battery to the lead cover of the cable and con¬ 
nect the other side to a galvanometer, voltmeter, electric bell, or telephone 
receiver. The wire running from the other side of the instrument used, 
should then be touched consecutively to every wire of the cable. No in¬ 
dication of an electric current is evidence that the wire under the test is 
broken. 

Crosses. —In testing for crosses, bunch all the wires, and connect 
them to one end of a testing circuit such as is described above; then re¬ 
move one by one the wires bunched, touching each successively to the 
other end of the testing circuit. The indication of an electric current 
shows that the wire touched is crossed with one of the other wires; said 
wire should then be marked and connected to the bunch and the test re¬ 
peated until nothing is left but crossed wires, when it is easy to determine 
between which wires the crosses exist; care must be taken to see that 
none o the wires are in contact with each other, or the lead cover at the 
far end of the cable. 

Crossed wires are located by the same methods used for grounded 
wires except that the post Gr. instead of being connected to ground is con¬ 
nected to the wire crossed, with the one used in the test. The localization 
of crosses is usually a more simple test than with grounded circuits, as 






298 


TELEPHONOLOGY 


the question of earth currents is entirely eliminated, and E. M. F.’s at the 
point of contact are of less common occurrence. 

Grounds .—If the fault is not due to a cross or open, the resistance to 
ground of the faulty wires, can be measured in the regular way, as if the 
unknown in the bridge was conductor resistance. The only exception be¬ 
ing that one of the X posts is connected to the faulty wire and the other 
to the ground. If the fault is due to the presence of moisture the resis¬ 
tance will become greater, the longer the battery is applied. 

The availability of a wire for a good return mate can be easily picked 
out by running over all the wires and having the testing set connected for 
insulation measurement. If a 100 pair cable is in trouble, it is possible to 
make a quick test of all the wires, in a few minutes and pick out the best 
and worst ones. 

The condition of the fault can be found practically by the use of a 
telephone and battery or direct current magneto. The reversed current 
magneto is not thoroughly reliable because it will ring when the electros¬ 
tatic capacity of the wire is sufficiently large. However, even with it, in 
the hands of an experienced man, low resistance faults can immediately be 
detected by the loudness of the ring and resistance to rotation of the 
handle. 

The methods first mentioned, however, are the most reliable and con¬ 
venient because they can be applied directly with the Testing Set. 

If the resistance of the fault is low, say 100 ohms or less, a few cells 
of battery will be sufficient to make an accurate location. If the resistance 
is over 1000 ohms an auxiliary battery of 25 or 50 cells may be needed. 
For very high resistance faults a reflecting galvanometer should be used 
in place of the testing set galvanometer. 

Two Faults on One Wire .—Having thus found and tagged the good 
and bad wires the next step is to make the connections for locating the 
fault. If the good and bad wires are of the same size and length the regu¬ 
lar Murray or Varley loop tests as described under the directions for ope¬ 
rating the Testing Sets can be applied, the first method being preferred. 

Sometimes, when making these tests, it is impossible to get a balance. 
This is generally an indication of two variable resistance faults at differ¬ 
ent points, or one of considerable extent, such as might be caused by the 
presence of moisture over 50 or 100 feet of cable. 

Under these conditions an accurate determination of the location of 
either fault is most unlikely. Generally speaking the calculated result 
will be nearest the fault of lowest resistance. In all cases the calculated 
distance must be somewhere between both faults but as there is no prac¬ 
tical way of finding the respective resistances of the faults, the probable 
location cannot even be estimated. The best plan of procedure is to make 
a rough measurement and calculation, cut the cable at this point, and then 
determine separately the distance to the fault in each section of cable. 

To find whether there are two faults on a faulty conductor, make tests 
from both ends and if the calculated locations are identical, only one fault 
exists, if different there are two or more. 

The effect of different fault resistance on the calculated results is il¬ 
lustrated in Figs. 363 and 364. Fig. 363 gives a diagram of the Murray 
loop test on a faulty wire containing two faults of resistances respectively 
x and y. 


TESTING EQUIPMENT AND FAULT LOCATION 299 

The resistance of both good and bad wires is 100 ohms each, and the 
resistance to the first fault is 50 ohms and to the second 90 ohms. As the 
distances and resistances are proportional we can discuss this problem by 
considering the resistances only. 



Fig. 364 shows a number of curves determined experimentally which 
give for certain definite values of x and varying values of y the corres¬ 
ponding resistance as calculated by the Murray loop formula which for 
this case, is: 


A 

Resistance = - x 200. 

A + B 

The resistance to the x and y faults are indicated by horizontal lines 
and it will be noted that for all values shown of x and y, the calculated re¬ 
sistances lie between these lines. 

The full line curves are for values of x used with the conections 
shown in Fig. 325. The broken line curves are for values of x used when 
the tests were made from the other end of the faulty wire. It will be noted 
that the test made from the two ends of the faulty wire with the same 
values of x and y always give different results, and that they differ most 
for low values of y. Also that when the resistance of one fault is high 
and the other low, the calculated resistance is nearest the fault of lowest 
resistance. 



Fig. 364. 


These curves are given more as an object lesson to show the great 
improbability of making a correct location of either of two faults on one 
wire. 

Correction for Lead Wires. —It sometimes happens that the testing 
instrument cannot be placed directly at the cable ends and it then becomes 
necessary to employ leading wires between the testing set and cable. 
When such is the case it is simplest to use leading wires of the same size 
as the faulty wire. Then the length of these leads must be added to L, the 































































300 


TELEPHONOLOGY 


combined length of the good and the bad wires, and from the calculated 
distance to the fault must be subtracted the length of the leading wire 
connected to the faulty wire. If the leading wires are different in size 
from the cable wires, then reduce them to the equivalent length of the ca¬ 
ble under test, as was explained for locating faults in circuits made up of 
two or more conductors having different sections. 

Check Tests .—In the regular and in some of the special applications 
of the loop tests, a check test can be made by reversing the good and the 
bad wires in the arms of the bridge. This change also requires a slight 
modification in the formula used for solving. 

Test Indicating Connections .—A simple method of determining 
whether a connection has been made at a distant point to a wire which 
can be connected to the testing set is as follows: 

Make preparations for a test of electrostatic capacity by the deflec¬ 
tion method and take discharge deflections before and after the connec¬ 
tion. If the latter is the greater a connection was made. 

This of course only applies when equipped with a more complete ca¬ 
ble testing set. 

Location of Opens .—When a conductor is actually broken and the re¬ 
turn circuit from the break is therefore of a resistance that is practically 
infinitely high, a new set of conditions are to be considered. In its loca¬ 
tion we depend upon the fact that any conductor, whether it is in a cable 
in the earth or submerged in water or an air wire, possesses “capacity” 
and is in fact a condenser of which it forms one plate with the insulation 
from the point of test to the break as the di-electric and the other plate 
being the earth or water. 

This capacity is proportional to the length of the conductor so by 
knowing its capacity per unit length, one procedure is to measure the 
capacity up to the break and convert it into the length of conductor. This 
method is open to the objection that the capacity is not always uniform 
throughout the length of a wire, as variations of 10% or more may occur. 
In measuring the capacity by this test, the deflection method is used in 
which the cable is charged with a certain potential, and the discharge is 
read by means of a reflecting galvanometer. If moisture is present, even 
in very small amounts, the deflection is liable to be augmented through 
the action of electrical absorption and the consequent return currents af¬ 
ter the instant of discharge. This phenomenon takes place in greater or 
less extent with all cables and increases with rise of temperature. 

A method, which largely removes the above objections and at the 
same time can be performed by a simple bridge arrangement, with the ad¬ 
dition of a telephone receiver and reversed battery current, is to compare 
the capacity of the open wire from the point of test to the open with the 
capacity of-the good mate. 

Referring to Fig. 365, if the capacities Cj and C 2 are the capacities 
of an open wire and its good mate respectively, we can balance these two 
capacities against R 1; and R 2 in the other two arms of a Wheatstone 
Bridge. Instead of a galvanometer, however, we make use of a telephone 
and a source of alternating current produced by one or more cells of dry 
battery.. If we adjust the resistances in the bridge so that no sound is 
heard in the telephone, then the points one and three will be at equal po¬ 
tential, and the cable capacities represented by <% and C 2 will be charged 
with the same difference of potentials, and will contain quantities propor- 



TESTING EQUIPMENT AND FAULT LOCATION 


301 


tional to their capacities; but the Quantities flowing into the condensers in 
the same time are inversely proportional to the resistances R, and R 
therefore, 



R 2 C, 

Rx C 2 

since capacity is directly proportional to the length and if L x and L, rep¬ 
resent the lengths of the open and good wires, then, 



The question of allowance for lead wires does not enter unless the 
leads are very long or where a wire in a cable may have to be used for a 
leading wire to the faulty cable. A method for allowing for extra long 
leads will be given under a description of the Fisher Portable Cable Test¬ 
ing Set No. 2. 







































302 


TELEPHONOLOGY 


The Leeds & Northrup Fault Finder .—This instrument has already 
been referred to on page — as a simplified form of Fault Finder. 

It has been designed with a view of reducing calculations connected 
with fault location to a minimum, also so as to simplify the manioulation 
as much as possible. It may be used to measure conductor resistance, to 
measure fault resistance, to locate faults by four distinct tests, and to lo¬ 
cate opens using a buzzer and telephone. 

Figure 366 shows the arrangement and connections of the resistance, 

etc. 



Fig. 367. 


The essential feature of the apparatus is the uniform resistance AB, 
Fig. 367, which is wound in a circle and is about 100 ohms. By a special 
construction, it is arranged so that contact can be made at any point along 
it, and it is therefore equivalent to a high resistance wire. It has a mov¬ 
ing contact C and a scale of 1000 divisions. In series with this, there are 
the two resistances E and R. E has exactly the same resistance as the 
wire AR. R has a resistance of 100 ohms, and is the rheostat of the 
bridge arrangement. Either resistance may be short-circuited by a small 
switch. The resistances shown between the ground post and the battery 
and between post Ba and the battery key are simply to protect the battery 
and the apparatus from excessive current. 

Resistance Measurement. —Fig. 367 shows the proper connections 
for measuring conductor resistance. As in the ordinary slide wire bridge 
the resistance X between the two posts X 1 and X 2 is gotten from the form¬ 
ula 


A 

X = - R 

1000 — A 


To avoid the necessity of solving in each case the fraction 



1000 — A 

















TESTING EQUIPMENT AND FAULT LOCATION 


303 


a table is furnished with the set, giving the value of this fraction for each 
value of A. The resistance is accordingly determined in each case by sim¬ 
ply setting the contact C for a balance and reading from the table the re¬ 
sistance opposite the number on the scale, and multiplying by 100. 

Example.—With an unknown resistance connected between the posts 
Xj and X 2 , the galvanometer showed a balance for a dial reading 387. The 
number opposite 387 in the table is .6313. Therefore, X = .6313 X 
100 = 63.13 ohms. 

Fault Locating With the Leeds & Northrup Fault Finder.—First 
Method.—Murray Loop. —This method is to be used in locating faults 
where there are two wires having equal resistance, in one of which there 
is a fault. Connect and set switches as shown in Fig. 368. Connect the 
good wire to post and the faulty wire to post X 2 . It will be remember¬ 
ed that E is equal to the resistance AB. From the symmetry of the ar¬ 
rangement, it will be obvious that the contact point C would rest for a bal¬ 
ance at 1000 on the scale, if the fault were exactly at the junction between 
the good and the bad wires; it would rest at 500, if the fault were half¬ 
way along the bad wire; and at whatever point it comes to rest, the read¬ 
ing divided by 1000 and multiplied by the length of the bad wire is the 
distance from the instrument to the fault. 



Example.—In a pair of equal wires, 5.8 miles long, one is grounded. 
With the connections made as shown in the diagram, the galvanometer 
balanced for the dial reading 124. The distance to the fault is 

124 X 5.8 

- = .7192 mile. 

1000 

Second Method Murray Loop. —This method is to be used for lo¬ 
cating faults where the good and the bad wires are. not equal to each 
other. The connections are shown in Fig. 369. It is the ordinary Mur¬ 
ray Loop and it will be readily seen that the resistance a to the tauL 
will be gotten from the formula 



a 


1000 




















304 


TELEPHONOLOGY 


where r is the resistance of the loop, and A is the reading of the contact C 
on its scale. The distance d to the fault is gotten from the formula 

A r 

d = - 

1000 M 

where M is the resistance per mile of the faulty wire. 



In some cases the value of M may not be known. In these cases de¬ 
termine the resistance of the faulty wire, which call R. This may be done 
by looping it with its mate, measuring the resistance of the faulty loop 
and dividing by two. 


R 

M = — 

L 

where L is the length of the faulty wire. Substituting this value for M in 
the above formula, we have 


L a r 

d = - 

1000 R 

Example.—A wire having a resistance of 16.46 ohms per mile had 
a ground in it. This was looped with a wire of unknown resistance and 
the total resistance of the loop was measured and found to be 54.07 ohms. 
Connections were made as in Fig. 369, and the reading A was found to be 
332. Substituting these values in the above formula, 

332 X 54.07 

d = - = 1.09. 

1000 X 16.46 

Third Method. Varley Loop .—This method may be used as a 
check on either of the above. Connect the faulty wire to X t and measure 
the resistance of the loop, then throw switches as shown in Fig. 370 and 













TESTING EQUIPMENT AND FAULT LOCATION 


305 


Let a — resistance to the fault, 
d = distance to fault in miles. 

M = resistance of faulty wire per mile, 
r == resistance of loop. 

R = resistance of coil R. 

A 

T = - (To be gotten from table). 

1000 — A 



Fig. 370. 

From the Wheatstone Bridge relation, 

r — R T r — 100 T 

T + 1 T + 1 

r _ 100 T 

d = - 

(T + 1) M 

Example.—A wire having a resistance of 16.46 ohms per mile had a 
ground in it. This was looped with a wire of unknown resistance and the 
resistance of the loop was found to be 54.07 ohms. Connections were 
made as in Fig. 370, and the reading A was found to be 234. From the 
table, T = .3055, and 


54.07 — 30.55 

d --- - = 1.094 miles. 

1.3055 X 16.46 

Fourth Method .—This method may be used to advantage where the 
length only of the faulty wire is known, and where there are two other 
wires which may be used to complete the loop. It is not necessary that 
the resistance and length of these other wires be known. Figs. 371 and 
372 show the connections. 

For the first measurement connect the faulty wire to X,, one of the 
good wires to X„ and the post Gr to ground; coils R and E, both short- 
circuited. Balance in the usual way and call the dial reading A. For the 















306 


TELEPHONOLOGY 


second measurement connect the post Gr to the other good wire as shown 
in Fig. 372, disconnect from ground and get another balance. Call this 
reading A 1 . The distance d to the fault is gotten from the simple formula 

A 1 

d = — L, 

A 

where L is the length of the faulty wire. 



Example.—All the wires in a cable 10852 ft. long were found to be 
grounded so that none of them could be used as good wires. Two wires 
were selected out of another cable going to the same place by a different 
route and securely joined to one of the grounded wires at the distant end. 
This grounded wire and one of the good wires were connected as shown 
in Fig. 371 and the reading A was found to be 307. Connections were 
the made as in Fig. 372 and A 1 was found to be 610. 



Fig. 372. 

Therefore, 

307 X 10852 

d = - = 5,462 ft. 

610 





















TESTING EQUIPMENT AND FAULT LOCATION 


307 


Location of Opens With the L. & N. Fault Finder. —These measure¬ 
ments are based on the fact that wires ordinarily have capacity which is 
proportional to their length. For a brief statement of the theory of the 
measurements see page . In addition to the Fault Finder a buzzer, dry 
cell to operate it, small induction coil, and telephone are required. These 
instruments are to be found in any telephone exchange. It is best to lo¬ 
cate the buzzer at some distance from the Fault Finder so that the opera¬ 
tor cannot hear it. 

General Remarks.—BeTore attempting locations for opens it is well to 
make two measurements. 

1st. The insulation of the broken wire and the insulation of the 
good wire with which it is to be compared. This may be done as describ¬ 
ed on page . It is best that the insulation resistance be fairly good, but 
experiments indicate that good results can be obtained by the following 
methods, even when it is as low as 100,000 ohms, and fair results when as 
low as 10,000 ohms to 50,000 ohms. 

2nd. The resistance between the two sections of the broken wire 
should be measured. This can be done by joining the broken wire and a 
good wire at the distant end of the cable and measuring the resistance of 
the loop. To insure close locations this resistance should be over 100,000 
ohms. Fair locations can be made when the resistance is much lower 
and it is worth while to attempt it even if the resistance is as low 
as 10,000 ohms. It must be remembered in cases where the resis¬ 
tance is less than 100,000 ohms that the distance to the open will actually 
be shorter than the test indicates. The amount by which it is short will 
be small for resistance near 100,000 ohms, and will become greater as 
the resistance decreases. The difficulty of determining the balance point 
also increases as the resistance decreases. 




Op r n Wire in a Telephone Cable. —The broken wire will be one of a 
pair. Select another pair in the cable that will have the same capacity 
per mile and join together the mate of the broken wire and one wire of 
the other pair. Connect the broken wire to the post Xj and the uncon¬ 
nected wire of the good pair to the post X 2 . Connect the buzzer to the 
primary of the induction coil, one terminal of the secondary to the post 
Ba and the other to the connected wires as shown in Fig. 373. Set switches 
so as to short-circuit the two resistance coils. Then depress the battery 
key and move the contact to the point of minimum sound in the telephone. 
































308 


TELEPHONOLOGY 


* 


The distance to the break is 


A 

d = L - 

1000 — A. 


where L is the length of the good wire. 

Examples.—A cable 1.45 miles long had a broken wire in it. It was 
found that the insulation resistance of the end of this wire was over 10 
megohms as was that of the good pair selected to test against it. The re¬ 
sistance between the two pieces of the good wire was also over 10 meg¬ 
ohms. Connections were made according to directions and it was found 
that the balance point was 476. From the table 

A 

- = .9084 

1000 — A 


and d = 1.45 X .9084 = 1.32 miles. 



Fig. 374. 

Open Wire in Telegraph and Other Cables in which the wires are 
not grouped in pairs. —Connect broken wire to X. Select a good wire and 
join to X 2 Connect all other wires and ground them, by connecting to the 
cable sheath. Connect the distant end of the broken wire to the others. 
Ground the end of the induction coil that is not connected to the post Ba. 
Make the measurement and calculation exactly as in the preceding case. 
See Fig. 374. 

The accuracy of the location by both of the above methods depends 
on the good and broken pair, or the good and broken wires having equal 
and uniform capacity per unit lengths. It is not always possible to select 
wires that are alike in this respect. In such cases, as for instance where 
there is no good wire in the cable containing the broken one and a good 
one has to be selected from another cable the following method may be 
used. 




























TESTING EQUIPMENT AND FAULT LOCATION 


309 


Broken Wire and Good Wire Not in Same Cable. —Connect the good 
wire and broken wire in the same way as shown in Fig. 373, (also de¬ 
scribed on page —), and set the pointer for a balance. Call the reading 
A. Then connect the good wire and the broken wire at the distant end 
and set the pointer for a new balance. Call this A 1 . The connections for 
this reading are shown in Fig. 374a. The distance to the break will be 

A A 1 L 

d = - 

1000 (A — A 1 ) + AA 1 

where L is the total length of the broken wire. 

Example.—A pair of wires containing one broken one was connected 
up with a good pair in a different cable as shown in Fig. 373. The read¬ 
ing A was found to be 180. The good and bad wires were then joined at 
the distant end as in Fig. 374a and the reading A 1 was found to be 88. The 
total length of the bad wire MN was 1.44 miles. 

180 X 88 X 1-44 

d = - = .211 miles. 

1000 (180 — 88) + 180 X 88 



To Use Galvanometer in Series With Battery. —Close both switches. 
Connect between posts Gr and X s . The galvanometer will have the maxi¬ 
mum sensibility with the pointer at 1000 and the minimum at zero 

To Pick Out Faulty Wires in a Cable. —Close both switches, set the 
pointer at 1000. Connect the post Gr to the ground or the cable sheath 
and apply the wires one after another to the binding post X... The gal 
vanometer will deflect for a faulty wire. 
































CHAPTER X. 


MEASURING INSTRUMENTS AND THEIR USES. 


*“Before proceeding to describe the various tests which may be made 
with the voltmeter, it is desirable to study more in detail its construction 
in order to comprehend how a sufficiently wide range of instruments to 
perform all tests can be secured. Fig. 375 shows the general appearance 
of the Weston instrument. If the case be removed, the magnetic system 
will be seen to consist of a powerful U-shaped magnet (Fig. 376), carry¬ 
ing the pole pieces, P P, which are bored out with great care, forming a 
hole about lVi, inches in diameter. In the centre of this is placed a piece 
of soft iron, C, carefully turned to leave a space of .04 inches between the 
poles in which the movable coil must swing. Fig. 377 shows the coil and 
pointer. The frame of the coil is of solid drawn aluminum, on which very 
fine wire is wound, the whole being only .015 inch think. The coil is sup¬ 
ported in sapphire bearings and supplied with light spiral springs made 
of non-ma^netic metal, serving to keep the needle under a constant and 
uniform tension. 



Fig. 375. Fig. 376. 


As it would be impracticable to place sufficient wire to secure the 
necessary resistance on the moving coil, a supplementary coil is placed in 
the case of the instrument. When the voltmeter is a double scale instru¬ 
ment, this coil is divided into two parts, the whole coil being placed in cir¬ 
cuit r or high voltages, and only a portion for low ones. Fig. 376 shows a 
skeleton view of a double coil instrument, the dotted lines showing the 
connection to the terminals, the coil in the base, and the moving coil. 

Consider now the action of the voltmeter in the light of Ohms’ law. 


*American Telephone Journal. 


( 310 ) 























MEASURING INSTRUMENTS AND THEIR USES 


311 


Assume an instrument of 1,000 ohms in the moving coil and 9,000 in the 
stationary one, total 10,000 ohms. Suppose this be connected to ten cells 
of storage battery, giving a known electro-motive force of 20 volts. The 
resistance of the wires from the voltmeter and the battery is so small in 
comparison with the 10,000 ohms of the instrument that they may be 
neglected, and taking Ohms’ formula we have E = 20 volts, R = 10,- 
000 ohms, 


20 

C = - = .002 amperes. 

10,000 

This is the current which passes through the voltmeter. The needle will 
deflect say about an inch, and as the battery gives 20 volts, we mark the 
point on the scale under the needle 20. If now we double the battery to 
40 volts, .004 ampere will flow, the needle will deflect half an inch and the 
scale be marked 10. Thus we see that where the voltmeter has a very 
high resistance compared to the source of electricity, the current which 
passes through it is exactly proportional to the voltage, and as the deflec¬ 
tions of the needle are proportional to the current they are equally propor¬ 
tional to the voltage. It would be just as easy to mark the point where the 
needle stands with ten cells, .002 amperes, or to mark it 20 volts. So that 
an instrument can be made, by properly graduating its scale, to read 
either a large number of volts or a small number of amperes. Suppose 
the 10,000 ohm instrument to be connected to an unknown source and the 
needle deflects 3 inches, we know by experiment that 1 inch on the scale 
means 20 or .002 amp., hence 3 inches mean 60 volts or .006 amperes. If, 
therefore, we know the resistance of any voltmeter and how much the 
needle moves for either a given number of volts, or a given number of am¬ 
peres, we can use it to measure either amperes or volts as we please. 



Fig. 377. 




._o« 

1 «WVW— 

Fig. 377a. 


So far the voltmeter has been assumed of constant resistance, but 
there is a supplementary coil which may be cut out at pleasure, and when 
removed the resistance is reduced from 10,000 ohms to 1,000. If now it 
be connected to the 20-volt battery the current will be 

20 

_ — .02 amperes, or ten times what flowed in the previous 

1,000 















312 


TELEPHONOLOGY 


v 

case. Hence the needle will be deflected (if possible) over ten inches in¬ 
stead of one inch and each scale division will have ten times the former 
value. With the supplemental coil in circuit, one volt or .0001 ampere 
was represented by one-twentieth of an inch. Without the coil one volt, 
.001 ampere, gives a deflection of one-half an inch. From these examples 
we deduce the following rules. 

First—The readings are proportional to the current which traverses 
the coil. 

Second—Any instrument may be graduated to read either in volts or 
in amperes, or both. 

Third—Instruments of large resistance will measure high voltages 
and very small currents, those of low resistance measure low voltages and 
large currents. Hence high resistance instruments are voltmeters and 
milliammeters and low resistance instruments are ammeters and milli- 
voltmeters. 

It is easy to see that these principles can be almost indefinitely ex¬ 
tended. Instead of winding the movable coil to a thousand ohms it may 
be wound to five hundred, one hundred, or even a fraction of an ohm. 
With each reduction in resistance, a larger current will flow with a given 
electrical pressure, or if the voltage is reduced there will still be sufficient 
current to give readable deflections. The best method of reducing resis¬ 
tance is to wind the instrument with heavy, coarse wire which will carry 
heavy currents without danger, and hence a voltmeter is transformed to 
an ammeter or current measurer by reducing the resistance of its coils 
and changing the figures on the scale. 

To test the condition of dry cells, the charge in a storage battery, or 
a cable for possible exposure to electrolysis, a low reading instrument is 
necessary. Such instruments are termed millivolt meters or milliamme¬ 
ters as the case may be, from the metric system prefix milli, meaning one 
thousandth. Thus the electrical engineer can measure either the electri¬ 
cal pressure of any source of electricity or the amount of current that is 
traversing any circuit. Equipped with a voltmeter and an ammeter he 
can measure both if he pleases, and knowing the current and the electro¬ 
motive force he can always calculate the resistance.” 

In Fig. 377a is shown the method of determining resistance with a 
voltmeter. 

The voltage of the battery is first noted by throwing the switch S in 
the upper position. The switch is then thrown in the lower position and 
the voltage through resistance R noted. 

The first measurement gives a deflection through the resistance of the 
voltmeter only, while with the switch in the second position, the deflection 
was through the resistance of the voltmeter plus the unknown resistance 
to be measured. If the voltmeter has a resistance of 10,000 ohms, and the 
first deflection was 10, and in the second instance the deflection was 5, 
then the unknown resistance is calculated as follows: 

Multiply the first deflection by the resistance of the voltmeter and 
divide this sum by the second deflection, then subtract the resistance of 
the voltmeter. 


MEASURING INSTRUMENTS AND THEIR USES 


313 


For instance.—In the example given above the first deflection was 
10. Multiply this by 10,000, which gives 100,000. Divide this by 5, 
which was the second deflection, which gives 20,000. Subtract from this 
the resistance of the voltmeter 10,000, which leaves 10,000 ohms, which 
is the unknown resistance. In this calculation the internal resistance of 
the batteries is neglected. This may be done in the case of high resistance 
measurements, as it would only amount to a few ohms. 

Expressed as a formula the above may be shown as follows: 

V = first deflection 
v = second deflection 
r = resistance of voltmeter 
X = unknown resistance. 

Vr 

Then X =-r 

v 

The Pignolet type o° instrument is shown in Fig. 378 and is often 
used in telephone work owing to its low cost and portability. For tele¬ 
phone work a combination instrument reading in volts and amperes is de¬ 
sirable. 



Fig. 378. Fig. 379. 


The voltmeter scale should read from 0 to 50 and from 0 to 5, and 
ammeter scale reading from 0 to 30. These instruments will measure 
volts, or volts and amperes and also determine resistance by a simple cal¬ 
culation, thus enabline one compact instrument to be used, not only for 
measuring current, but for ascertaining the resistance of coils, circuits, 
etc., detecting and locating grounds and short circuits, and in addition for 
measuring mil-amperes up to 30 or 50. 

The instrument is so adjusted that each division of the voltmeter 
scale is equal also to one mil-ampere (0.001) and an instrument reading 



















314 


TELEPHONOLOGY 


to 5 volts has 100 ohms resistance; 10 volts 200 ohms; 25 volts 500 ohms; 
50 volts 1,000 ohms; 100 volts 2,000 ohms. 

This adjustment permits resistance to be ascertained by Ohm’s law 
that the resistance of a circuit is equal to the volts divided by the amperes 
R = E -r- I. To apply the law with the instruments, first measure the 
volts of the battery used for the test, then ascertain the amperes with the 
unknown resistance in circuit with the instrument and the battery. Divide 
the volts by the amperes, which gives the resistance of the circuit includ¬ 
ing the resistance of the voltmeter; subtract the resistance of the voltme¬ 
ter and the remainder is the unknown resistance. 

For Example.—Suppose the instrument to read 5 volts in tenth scale 
divisions and to have a resistance of 100 ohms, the battery to have a 
pressure of 4.5 volts and the mil-amperes to be 20, indicated by the deflec¬ 
tion of the pointer of 20 scale divisions, when the unknown resistance is 
connected in circuit. Then the unknown resistance equals 4.5 volts divid¬ 
ed by 0.020 amperes (20 mil-amperes) less 100 ohms (the resistance of 
the instrument) which gives 125 ohms as the unknown resistance. 

With an instrument reading to 50 volts and having a resistance of 
1,000 ohms: if the battery pressure were 40 volts and the mil-amperes 
were 5 when the unknown resistance was in circuit, the unknown resis¬ 
tance would be equal to 40 volts divided by 0.005 (5 mil-amperes) less 
1,000 ohms (the resistance of the instrument) which gives 7,000 ohms as 
the answer. 

These examples illustrate the method, and the following tables indi¬ 
cate its capacity or range. The range of measurements for a single instru¬ 
ment may be increased by combining a low and high reading voltmeter in 
one instrument. For example, 0 to 3 volts and 0 to 50 volts. 

The resistance of the battery used for the test is included in the cir¬ 
cuit when the measurements are made. The battery should therefore be 
one of comparatively low internal resistance so that it will not appreci¬ 
ably affect the results when low resistances are being measured. The or¬ 
dinary small dry batteries answer very well for the purpose. 

As it is apparent, this method has not the accuracy nor the range of 
the Wheatstone bridge, but it answers admirably for ordinary purposes, 
and adds largely to the usefulness of a voltmeter or volt-ammeter. 

The following table shows the scale dimensions for which the 
pointer is deflected, with the various battery pressures as shown, through 
the resistance as given: 


Deflection of 

Pointer of BATTERY PRESSURE. 

Instrument. 



4.5 Volts 

22.5 Volts 

45 Volts 

90 

40 divisions 

112.5 ohms 

62.5 ohms 

125 

ohms 

250 

36 

25 

125 

250 

u 

500 

30 

50 

’ 250 

500 

it 

1,000 

22. 

100 

500 

1,000 

n 

2,000 

15 

200 

1,000 

2,000 

a 

4,000 

11.25 “ 

300 

1,500 

3,000 

a 

6,000 

7.5 

500 

2,500 

5,000 

a 

10,000 

5 

800 

4,000 

8,000 

u 

16,000 

3 

1,400 

7,000 

14,000 

a 

32,000 

2 

2,150 

10,750 

21,500 

a 

43,000 

1 

4,400 

22,000 

44,000 

u 

88,000 


Volts 

ohms 









MEASURING INSTRUMENTS AND THEIR USES 


315 


It will thus be seen that a resistance as high as 88,000 ohms can be 
measured with a pressure of 90 volts, which can easily be obtained in or¬ 
dinary exchanges where a pole charger is used, as the pole charger bat¬ 
teries can be used for operating the voltmeter. 

The simplest measurement that can be made with a voltmeter is to 
measure battery pressure or voltage. This is accomplished by connecting 
the terminals of the battery directly to the terminals of the instrument, 
as shown in Fig. 380. An ordinary dry cell in good condition will give 
from 1-4/10 to 1-6/10 volts. 

Always connect the batteries to the high scale first, then if the read¬ 
ing is within the limit of the low scale, arrange the connection so as to 
read the low scale. The wire from the carbon pole of a battery should al¬ 
ways connect to post marked “P.’ Do not reverse the current or the 
pointer may be bent. 

We will suppose that a resistance, such as an ordinary drop coil is 
to be measured. First measure the volts of the battery by connecting the 
battery directly to the voltmeter, as shown in Fig. 380. In this instance 
we will suppose the battery to equal 4-5/10 volts. Then connect the bat¬ 
tery and the drop coil to the voltmeter as shown in Fig. 382. In this in¬ 
stance suppose the pointer moves over 20 scale divisions, which repre¬ 
sents 20 milli-amperes. The resistance of the voltmeter is known to be 
100 ohms. The various figures are set down as follows: 


Hr 1 

Vn 1 

- - 



i 

Me as* ri\ 

HOs 

Tramp 



38 0 


4.5 -r- .020 = 225. 



r/6 38/ 





The unknown resistance o" the voltmeter is 100 ohms, and this 
should be subtracted from the result which leaves 125 ohms, the resis¬ 
tance of the drop coil. 

The resistance of various lines can be measured by this method. Here 
a stronger battery should be used. If it is desired to know the insulation 
resistance of a line, the line, battery and voltmeter should be conected as 
shown in Fig. 383. Proceed exactly as before and the result will be the 
leakage from the line to the earth. 

In making this test, in some cases it will be seen that “earth current 
will exist which will deflect the voltmeter, and when the presence of an 
“earth current” is suspected, it is best to connect the instrument directly 
to the line and the earth without the battery and note the deflection. Ihen 
connect the battery in circuit as shown, in such a manner the eaith cur- 











































































































316 


TELEPHONOLOGY 


rent and battery do not oppose each other. Then subtract the number of 
degrees which the earth current deflected the pointer, from the number of 
degrees which the pointer is deflected by both the battery and the earth 
current: the difference will be the true voltage used in measuring the re¬ 
sistance of the line, and the calculation should be based on this. 

In this case the high scale of the instrument should be used with as 
much battery as possible, so as to secure as great a deflection as possible. 

To measure high resistance such as bridging ringer coil, etc. Con¬ 
nect as shown in Fig. 382, using 20 or more cells of battery, connecting 
wire from coil to “50” instead of “5” if deflection is too great for the 5 
volt scale. 



Fig. 385. Fig. 386. 


In telephone work an instrument reading from 0 to 50 volts, with a 
resistance of 45,000 ohms, is desirable. The instrument manufactured by 
the Weston Company is so sensitive that by placing the fingers across the 
terminals of a 24 volt battery and the voltmeter in series, a deflection of 10 
or 15 volts will be shown. This instrument is especially desirable for 
quickly measuring line resistance and is very accurate. 

Voltmeters, milli-voltmeters, ammeters and milli-ammeters have the 
same general appearance, the difference being in the resistance and man¬ 
ner of dividing the scale. The standard portable instrument shown in Fig. 
385 is recommended for use where a standard instrument of the highest 
accuracy is desired combined with portability. It is well where a num¬ 
ber of voltmeters are used by one company, to have an instrument of this 
description to check the others. 

This is accomplished by connecting the battery and voltmeters as 
shown in Fig. 386. Both instruments should indicate the same unless 
they differ widely in resistance, which is not usually the case. 



Fig. 387. 


The standard instrument described above is equipped with spirit 
level for accurately placing the instrument, and a scale 12 inches in 
length, pointer 8-1/4 inches. The divided lines of the scale are connected 


















MEASURING INSTRUMENTS AND THEIR USES 


317 


together by means of diagonal lines drawn through six arcs placed equal¬ 
ly distant from each other, as shown in Fig. 387. This arrangement per¬ 
mits the position of the pointer to be read directly to 2/10 of a scale divi¬ 
sion. 

The accuracy of measurement obtainable with this set is 1/10 of 1%, 
and in the instrument of three ranges, viz. 0 to 150, 0 to 15 and 0 to 3 
volts, the indications are readable in the first instance to 1/5 volt, in the 
second to 1/100 volt and in the third to 1/500 volt. 




Fig. 388. Fig. 389. 

Where it is possible- to permanently fix the instrument in one place 
the Weston Round Pattern Meter is desirable. This instrument is adapt¬ 
ed for mounting on the iace of the switchboard, and is shown in Fig. 388. 
Where a flush type instrument is desired, the Round Meter shown in Fig. 
389, may be used, a hole being made in the switchboard or other place 
where the instrument is mounted so that the face of the voltmeter is flush 
with the surface. 



Fig. 390. 

For exchanges using pulsating current for selective party line ring¬ 
ing, a double scale instrument, as shown in Fig. 390, is often desirable. 
Here the 0 is placed in the centre of the scale, and the scale reads both to 
the right and left. This enables the instrument to be permanently con¬ 
nected to a jack and readings taken by plugging in and throwing the vari¬ 
ous keys as desired, without having to reverse the voltmeter. 





318 


TELEPHONOLOGY 


Fig. 391 shows in detail the design of the supporting bracket, core 
and one pole piece of the American Inst Co.’s voltmeter. Strength and 
simplicity of design will be noted in the supporting bracket, which is a 
one piece casting. The pointer is counterbalanced by delicate screws of 
the grade used in high grade watches. A cylindrical steel pivot supports 
the moving coil. 



Fig. 391. Fig. 392. 


One feature which may be especially mentioned in connection with 
these instruments is that all milli-voltmeters intended for use as amme¬ 
ters with external shunts, are adjustable to a uniform resistance of one 
ohm, and give full scale deflection with a potential difference of 50 milli- 



Fig. 393. Fig. 394. 


volts and are therefore interchangeable. This means that any shunt can 
be used with any milli-voltmeter. The interior construction of these in¬ 
struments is shown in Fig. 392 which is typical of the interior arrange¬ 
ment of the various parts in nearly all makes. 













MEASURING INSTRUMENTS AND THEIR USES 319 

The portable type of instrument particularly adapted to telephone 
use is shown in Fig. 393, and this instrument with a range from 0 to 50 
volts has 1/2 volt divisions and may be read to a tenth. 

The laboratory type of this make of instrument is shown in Fig. 394. 
It will be noticed that the scale is particularly wide and the divisions uni¬ 
form throughout. 

The Whitney Company in their line of instruments present a differ¬ 
ent form of construction from that just described. See Fig. 395. 



To the movable coil “A” are attached ruby jewels “B” of the kind 
used in high grade watches. Through the holes pierced through these 
two jewels, is threaded a length of prosphor bronze or steel wire “C’\ 
which thus guides the coil and holds it truly centered. To prevent end¬ 
wise motion two spiral springs D and D 1 are attached to the coil the other 
ends of same being attached to brackets on the stationary part of the in¬ 
strument. These springs not only support the coil, but furnish the force 
opposing its rotation when the current flows. If the instrument is so 
built the coil A will slide up and down for a short distance without caus¬ 
ing any damage. 

The above will serve to illustrate the various types of instruments in 
general use. It should be understood that any make of volt-meter may be 
used in testing, provided its range is suitable for the purpose. 

The polarity of a current can be ascertained by connecting the cir¬ 
cuit to the terminals of the volt or ammeter if the instrument is of the 
type using a permanent magnet and moving coil, such as the Weston or 
American. There are, however, some types of instruments of the electro¬ 
magnetic type, in which the permanent magnet is not used, and these will 
not show the polarity of the current under test. Therefore in making 
tests for polarity the instrument should be tested (if the type is not 
known) and it should be positively determined that the instrument will 
only deflect in one direction when connected. 

The + or positive side of the majority of instruments is usually the 
right, looking at the meter from the front, and this is marked -f- or P. Do 
not reverse the instrument or damage may result. 


































320 


TELEPHONOLOGY 


*“The difference between a volt-meter or pressure measure, and an 
ammeter, or current measure, has been described and shown to be chiefly 
in the method of winding the moving coil that forms the active portion of 
the instrument. There is still another way of making ammeters, which 
will presently be described; but prefatory thereto let us consider a little 
the use of the ammeter and the method of measurement to which the 
joint use of both an ammeter and volt-meter lend themselves. There are 
many makes of volt-meters, but relatively few of ammeters, particularly 
of those of high range, as their construction practically presents much 
more difficulty on account of the heating effect of large currents. The 
chief external difference between a volt-meter and ammeter lies in the 
binding posts, which in the ammeter are very large and heavy, to accom¬ 
modate the powerful leads necessary to carry heavy currents. The office 
of the ammeter is solely to measure the amount of current which is pass¬ 
ing in any circuit. For this purpose the circuit whose current is to be 
measured must be open and the ammeter inserted in series so that it 
forms an integral part thereof through which all the current must flow as 
soon as the circuit is closed. After the insertion of the instrument a read¬ 
ing of the needle indicates at once the current in amperes—nothing could 
be simpler. Evidently the resistance of the ammeter must be very low, so 
small, in fact, that it’s addition to any circuit will cause no appreciable 
change. Like volt-meters ammeters can only be built to cover a some¬ 
what limited range in a single instrument, but by getting two or more, 
any capacity can be secured. For the telephonist the most useful instru¬ 
ment is one reading to about 50 amperes, each scale division representing 
1/2 ampere. 

Some methods of measuring high resistance with a volt-meter have 
been described. There are many cases in telephone work where it is 
necessary to measure very small resistance, such for example, as would 
be presented by the blades of a knife switch upon a power board which 
fail to make good contact. With an ammeter and a milli-volt-meter low 
resistance of all kinds can be very readily and very accurately measured. 
The operation consists of connecting the battery, the low resistance to be 
measured and the ammeter in series and noting the amount of current 
which flows. At the same time a milli-volt-meter is connected around the 
resistance so that the fall of potential, or the electromotive force which is 
required to force the current through the resistance is also measured. 
When these two quantities are known, two factors, namely, the electro¬ 
motive force arid the current, in Ohms’ formula, are obtained, and it is 
easy to calculate the third. The telephonist has frequent occasions to 
measure the resistance of very large and heavy conductors, such as the 
bus bars on the back of a switchboard, which might be giving rise to cross 
talk, or the various connections of a common battery through the power 
switchboard, and its numerous instruments, to the circuits which distrib¬ 
ute electrical energy to the telephone switchboard. The method just de¬ 
scribed is exceedingly convenient for the purpose. It is illustrated in Fig. 
396, in which C B is a portion of a bus bar or other large conductor whose 
resistance is desired. B is a storage battery or other source of electrical 
supply, one pole of which is connected to the bus bar, C, while the other 
pole runs to one binding post o s the ammeter, Am. From the other ter¬ 
minal bar a conductor is taken to the other end of the bus bar. At each 
contact on the bar care must be taken to make an exceedingly good con- 


*American Telephone Journal. 




MEASURING INSTRUMENTS AND THEIR USES 


321 


tact, so that there may be as little fall of potential between the leads and 
the resistance to be measured as possible. A milli-voltmeter, mVm, is 
attached to the bus bar at the points C and B, between which the resis¬ 
tance is desired. Now the reading of the ammeter shows the amount of 
current which flows through the bus bar. A simultaneous reading of the 
milli-voltmeter gives the fall of potential between the points to be meas¬ 
ured for resistance, or, in other words, the electromotive force that causes 
the current indicated by the ammeter. For example: Suppose it is de¬ 
sired to measure the resistance of a copper bus bar *4" in diameter and 
that when the apparatus is arranged, as shown in Fig. 396, the ammeter 
shows a reading of 21/2 amperes and the milli-voltmeter a reading of 5 
milli-volts, the resistance is given by the expression 
.005 


R = - = .0002 ohms 

2.5 



Fig. 396. 



The same method may be very conveniently applied to the measure¬ 
ments of the resistance of dynamo armatures. Thus, in case of any 
trouble with the charging generators of a telephone power plant, this plan 
forms a convenient way of detecting the existence of either a short circuit 
or open coils. The apparatus should be set up as shown in Fig. 397, one 
pole of the storage battery being applied to any commutator section, the 
other pole running to one terminal of the ammeter, Am. From the other 
binding post o* the ammeter a lead is carried to the commutator section 
directly opposite to the first one. The milli-voltmeter is connected to the 
same two sections, as shown in the illustration, and from the simultan¬ 
eous readings of the two instruments the resistance of the armature and 
its coils may be at once calculated. To test all the coils of a dynamo the 
contacts may be arranged as sliding springs and the armature slowly re¬ 
volved under the contacts and thus faults at once detected. 

Fig. 398 shows the further application of this method to the meas¬ 
urement of switch resistance, an exceedingly interesting investigation to 
the telephonist, as in many cases poor hinges and bad blade contacts may 
give rise to cross talk in the operators’ transmitters or even in the sub¬ 
scribers’ circuits. As shown in this illustration, the ammeter is connect¬ 
ed in series with the switch terminals and the battery, while the milli- 
voltmeter is connected across the terminals, and the resistance of the 
switch can be ascertained as soon as the two instruments are read. Tn Fig. 

21 


1 






















































322 


TELEPHONOLOGY 


399 this method is shown applied to measure the resistance of a switch¬ 
board ammeter, such as is commonly supplied to power boards in common 
battery exchanges, for occasionally a contractor will install an instru¬ 
ment of so high a resistance as to be unsuitable for the purpose, and 
sometimes the ammeter contacts become loosened and introduce sufficient 
resistance to cause cross talk. The circuit in Fig. 399 is self-explanatory. 
In the measurements of small resistance we have assumed an ammeter 
capable of reading a considerable current and a milli-volt-meter adapted 
to read small differences of potential. But this method may be extended 
to embrace the measurement of large resistances by the use of a milli-am- 
meter capable of measuring small current and of a voltmeter capable of 
measuring large differences of potential. 

To illustrate this modification, suppose a case in which the voltmeter 
should read 142 volts and the milli-ammeter 10 mil-amperes, 

142 

R = - = 14200 ohms. 

.01 



Fig. 398. Fig. 399. 


From these illustrations it is evident that the possession of a milli- 
voltmeter and a milli-ammeter and an ammeter and a voltmeter will en¬ 
able the electrician to make a very wide series of measurements, for with 
the milli-ammeter and ammeter currents of almost any range can be 
measured. The voltmeter and the milli-voltmeter enable the estimation 
of electromotive force through a correspondingly great latitude, and with 
both instruments all sorts of resistance measurements can be made.” 

The resistance of voltmeters can be found stajnped on the case, or if 
not, write to the makers giving the serial number of the instrument. 

In case it becomes necessary to find the resistance of the voltmeter, 
proceed to connect up the voltmeter, battery, and a resistance box in se¬ 
ries. First take the voltage of the battery without resistance in circuit. 
Suppose this should be 20 volts, then implug enough resistance to make the 
reading exactly 10 volts, or one half the first deflection, the resistance im- 
plugged will then equal the resistance of the voltmeter. Where the same 
battery is always used for making tests, it is not necessary every time to 







































measuring instruments and THEIR USES 323 

make a calculation, but if the voltage of the battery remains constant, a 
table can be prepared showing the value of each scale division in ohms. 
One of the most useful applications of the voltmeter to telephone 

Jeverv^ Zi°T™ °l ^ troubles ‘ It well to take a reading 

Wp G r by Sh ° rt circuitin £ the bne at the telephone. 

We will assume that the line measures 100 ohms. A record should be 

made ot this, and if at any time a subscriber complains of trouble, corres¬ 
ponding measurements can be made, and if it is found that the line has in¬ 
creased materially in resistance, it is safe to assume that there is a bad 
splice or other defect on the line. 

In common battery work, high resistance voltmeters, reading from 
0 to 50 with a resistance ot 45,000 ohms are adopted for readily deter- 
minmg the condition of condensers. The instrument can be connected 
with a key as shown in Fig. 400. When the key is thrown, the condenser 
is charged and discharged, and the voltmeter will give a “kick” of about 
10 volts when a 24 volt battery is used and the condenser is of 2 M F 
capacity. ' * 



The “kick” is proportional to the capacity. In other words: if a 1 
M. F. condenser was used in place of the 2 M. F. the “kick” would only be 
5, a Vg M, F. condenser 21/2 and so on. This is especially valuable when 
testing four party lines. 

When all four parties are connected there are four condensers con¬ 
nected across the line. If one of these parties should be “lost” by reason 
of the tap from the main line getting open, it is only'the work of an in¬ 
stant to determine definitely that one of the parties is “lost” if the “kick” 
with all on the line has been noticed, as a decrease will be apparent. 

As a line has some capacity, it can be roughly determined in the case 
of a long line whether the “open” is near the office or at the extreme end, 
by observing the capacity “kick” of the voltmeter. If the “open” is near 
at hand no perceptible “kick” will result, but if a considerable length of 
open wire is connected to the voltmeter a “kick” will result in proportion. 
A little practice will enable accurate judgment to be exercised, but close 
observation is necessary, as the movement of the pointer is very small. 
Satisfactory results can only be obtained when the line is absolutely free 
from grounds or short circuits. 

*“We have just shown how all kinds of resistance may be tested by a 
simultaneous measurement of the current passing, and by the fall of po¬ 
tential on the ends of the conductor whose resistance is desired. Evident¬ 
ly if the resistance of the conductor be known, a single measurement with 
a voltmeter or milli-voltmeter will suffice to determine the current 
strength, and thus amperes can be measured with a voltmeter. This is 
shown in Fig. 401. Suppose R to be any known resistance, and assume V 
to be the reading of the needle, then the currrent is: C= V -i- R. 


^American Telephone Journal. 












324 


TELEPHONOLOGY 


For example, suppose a wire chief wishes to know the current taken 
from the office battery at the hour of maximum load. Assume the power 
switchboard bus bars to be 10 feet long 14 inch thick and 1 inch wide. 
Such a bar has an area of 250 square inches. One square inch is 1,273,- 
236 circular mills. A piece of copper one circular mil in diameter and one 
foot long has a resistance of 9.012 ohms, but in the bus bar there are 318,- 
309 circular mills, hence the resistance is 

90.12 

- = .0002831 ohms. 

318,309 

Suppose the reading on a milli-voltmeter connected to the end of the 
bar to be 15 milli-volts, then 

.015 

C = - = 47.75 amperes. 

.0003142 

There are numberless opportunities to utilize this plan, that will at 
once occur to the practicing electrician. Indeed all ammeters intended to 
read very large currents take advantage thereof. 




To return to the tests to be made with the voltmeter for a moment; 
there is a handy method for general resistance measurements of medium 
amounts, such as ringer spools, receiver coils, relays, induction and re¬ 
tardation coils. Set up the apparatus as shown in Fig. 402. B is any con¬ 
venient battery, R is the unknown resistance to be measured, R l is any 
known resistance and V m is the voltmeter. First connect the voltmeter 
around R\ and read the needle, calling the deflection V ; then connect in 
the same way around R and read again, getting a deflection V 1 ; then 

R 1 X V 

R: R 1 :: V: V 1 or R = - 

V 1 

Example.—Suppose R 1 = 110 ohms, V 1 = 15 volts, V == 5 volts, 

110 X 5 

then - R = - = 36.7 ohms. 

15 




1 




































MEASURING INSTRUMENTS AND THEIR USES 


325 


In this method both upper and lower scales of the voltmeter can be 
used to secure a very wide range, thus, let R 1 — 550 ohms V 1 (in upper 
scale), = 148 volts; V (on lower scale) = 3 volts, 

550 X 148 

thus R = - = 2,710 ohms; or let R 1 = 550 ohms, V (on 

3 

lower scale) — 3 volts; V 1 (on upper scale) = 148 volts 
550 X 3 

thus R = - = 11.16 ohms. 

148 

A modification of this method, which has already been alluded to, 
consists in substituting an ammeter for the coil of known resistances, and 
reading both instruments. This is illustrated in Fig. 403 in which B is 
the battery, A m the ammeter in series with it and the resistance to be 
measured R, while V m is the voltmeter placed around the resistance as 
before. 



Thus R = -in which V is the volt-meter reading andA the ammeter. 

A 

Example.—Suppose we wish to measure an induction coil; when 
connected up as shown A = 3 amperes, V = 12 volts, then 

12 

R = - = 4 ohms. 

3 

The telephonist often must know the internal resistance of a battery 
or other generator of electricity. This is somewhat of a difficult task, as 
the thing to be measured is the source of the current and electromotive 
force used in measuring. It is a kind of “lifting yourself by your boot 
straps” problem. But with a voltmeter, a known resistance and a switch 
it can be done. Set up the apparatus as in Fig. 404, in which E is the bat¬ 
tery of which the resistance is desired, R the known resistance, I on the 













































326 


TELEPHONOLOGY 


voltmeter and K a key or suitable switch. Read the voltmeter with K 
open, call the reading E, close K and re-read, calling the second deflec¬ 
tion e. Then if r is the desired resistance of the cell 

R X E —e 
r = - 

e 

Example*—Suppose the case of some dry cells R = 4 ohms, E = 1.5 
volts, e = 1.35 volts then 


1.50 — 1.75 

r = - = .44 ohms. 

1.35 

This method is liable to be about 5% or 6% in error. If more accurate 
work is desired the following plan may be used, which requires three re¬ 
sistances, one of which must be a variable one. Connect as shown in Fig. 
405 in which E is the battery to be measured, R 1 and R 2 are any two re¬ 
sistances, R 3 a variable resistance like a resistance box, and K a switch 
which can be placed in contact with either B or C. Adjust R 3 till the de¬ 
flection of the voltmeter remains the same whether K is placed on B or C, 
then the resistance of E is exactly equal to R 3 and no calculation is neces¬ 
sary. Here is a third method of exceeding simplicity. Connect a voltme¬ 
ter (low reading one) in series with the battery and a variable resistance 
so adjusted as to give a large deflection R\ Increase the variable resis¬ 
tance of R 2 till exactly half the first deflection is produced. Then if r is 
the resistance of the voltmeter and R is the desired battery resistance, 
R=R 2 —2 R 1 -f- r. For example: In the case of a gravity cell r= 1 ohm, 
R 1 16.25, R 2 = 35.5, the R = 35.5— (2 X 16-25 + 1) = 2 ohms.” 



Fig. 3 







Hftira. ^ 


Fig. 4' 


iz£$z 


Fig. 1 


f 


Fig. 2 



Fig. 5 


Fig. 7 


Complete Ammeter and Details 

Fig. 406. 


For those who desire to experiment with a view to investigating the 
construction of voltmeters and ammeters, and thereby become more fa¬ 
miliar with their principle of operation, the following instructions will 


































































MEASURING INSTRUMENTS AND THEIR USES 


327 


prove interesting. The instrument is fairly accurate if carefully made, 
and will serve fairly well for rough and comparative tests. The figure 
numbers refer to the various parts of Fig. 406. 

*“The only adjustment necessary is that of leveling, which is accom¬ 
plished by turning the thumb screw shown at A, Fig. 1, until the hand 
points to 0 on the scale. 

First make a support, Fig. 2, by bending a piece of sheet brass to the 
shape indicated and tapping for the screws, C C. These should have hol¬ 
low ends, as shown, for the purpose of receiving the pivoted axle which 
supports the hand. The core, Fig. 3, is made of iron. It is 1 in. long, 1/t 
in. wide and Vs in. thick. At a point a little above the center, drill a hole 
as shown at H and through this hole drive a piece of knitting needle about 
V 2 in* long, or long enough to reach between the two screws shown in Fig. 
2. The ends of this small axle should be ground pointed and should turn 
easily in the cavities, as the sensitiveness of the instrument depends on 
the ease with which this axle turns. 

After assembling the core as shown in Fig. 4, it should be filed a lit¬ 
tle at one end until it assumes the position indicated. The pointer or 
hand, Fig. 5, is made of wire, aluminum being preferable for this purpose, 
although copper or steel will do. Make the wire 4^2 in. long and make a 
loop, D, 1/2 in* from the lower end. Solder to the short end a piece of 
brass, E, of such weight that it will exactly balance the weight of the 
hand. This is slipped on the pivot and the whole thing is again placed in 
position in the support. If the pointer is correctly balanced it should take 
the position shown in Fig. 1, but if it is not exactly right a little filing will 
bring it near enough so that it may be corrected by the adjusting screw. 

Next make a brass frame as shown in Fig. 6. This might be made of 
wood, although brass is better, as the eddy currents set up in a conductor 
surrounding a magnet tend to stop oscillation of the magnet. (The core 
is magnetized when a current flows through the instrument.) The brass 
frame is wound with magnet wire, the size depending on the number of 
amperes to be measured. Mine is wound with two layers of No. 14 wire, 
10 turns to each layer, and is about right for ordinary experimental pur¬ 
poses. The ends of the wire are fastened to the binding-posts, B. C, 
Fig. 1. 

A wooden box, D, is then made and provided with a glass front. A 
piece of paper is pasted on a piece of wood, which is then fastened in the 
box in such a position that the hand or pointer will lie close to the paper 
scale. The box is 51/2 in. high, 4 in. wide and 1% in. deep; inside meas¬ 
urements. After everything is assembled put a drop of solder on the loop 
at D, Fig. 5, to prevent it turning on the axle. 

To calibrate the instrument connect as shown in Fig. 7, where A is 
the home-made ammeter; B, a standard ammeter; C, a variable resistance 
and D a battery, consisting of three or more cells connected in multiple. 
Throw in enough resistance to make the standard instrument read 1 Amp. 
and then put a mark on the paper scale o : the instrument to be calibrated. 
Continue in this way with 2 amperes, 3 amperes, 4 amperes, etc., until the 
scale is full. To make a voltmeter out of this instrument, wind with plenty 
of No. 36 magnet wire instead of No. 14, or if it is desired 10 make an in- 


*Popular Mechanics. 



328 


TELEPHONOLOGY 


strument for measuring both volts and amperes, use both windings and 
connect to two pairs of binding-posts.” 

*“The Galvanometer is an instrument similar in construction to the 
voltmeter. The uses of the galvanometer have been discussed in Chapter 
IX and commercial instruments may now be purchased so cheap that little 
excuse is offered for any one to build them. The construction of a Galvano¬ 
meter is however, interesting, and helps to a thorough understanding of 
the principle of operation. 



Fig. 407. 


Fig. 408. 


“An old telephone generator furnishes excellent magnets for the con¬ 
struction of such a galvanometer. A magnet which a writer in Popular 


♦Popular Mechanic. 





























































































































































MEASURING INSTRUMENTS AND THEIR USES 329 

Mechanics secured from such a source measures 6 inches in length and is 
made of steel, which is 1/2 inch by 5/8 inch. The more powerful the 
magnet the better. Its dimensions may vary somewhat from the one used 
in the following paper, but the reader can easily modify his instrument to 
suit his needs. 

A bottomless box with a glass top will be required, mounted upon a 
base board, the whole being suited to be screwed to the wall, as shown in 
Fig. 407. This box is 7 inches by 12 inches outside measurement, and 41/2 
inches deep. The base board should be 151/2 inches by 8Vo inches. The 
box is secured to the base board by two hasps, one on either side, two or 
three dowel pins helping to hold the box from slipping. This method of 
securing the box is adopted so the case may be easily removed, giving ac¬ 
cess to the working parts of the instrument inside. 

The magnet used being 5/8 inch wide, two pieces of iron, shown at P, 
are made for pole pieces. These are % inch square and 1% inches long 
and have bored through them two holes 1/8 inch in diameter, through 
which are to pass screws which are to secure them in place. Secure the 
magnet firmly to the base board, its poles being 9 \\ inches from the bot¬ 
tom, and at equal distances each side of the centre line. A block of wood 
at eacii side of the magnet, another at the bottom, and two clamps, one at 
each side, ought to secure the magnet firmly in place so that it cannot slip. 
Then screw the pole pieces into place, taking care that they rest firmly 
against the inner poles of the magnet. This will leave 1 1-16 inch of clear 
space between the poles, if the dimensions given have been followed. If 
the magnet used has dimensions differing from those given at M, Fig. 408, 
allowance will have to be made in the pole pieces, so as to leave the proper 
space between the pole pieces. 

In the exact centre of this space is to be secured an iron cylinder, 
shown in Fig. 407 and also at C in Fig. 408. This is % inches long % 
inch in diameter. It is to be fastened to the base board by a screw pass¬ 
ing completely through it. This should leave a clear space of 1/32 inch 
on each side of the cylinder. It is well at this point to take a very small, 
sharp chisel and cut two grooves in the base board, these grooves being 
extensions backward of the spaces between the poles and the cylinder on 
each side. These grooves are necessary in order to allow the coil shown 
in Fig. 407 to swing freely in either direction without striking the back 
board. i J 

Take next a piece of the thinnest copper procurable. It should be very 
thin in order to be light and to take up as little space as possible. From 
this sheet copper make a frame such as is shown in Fig. 408. It is rect¬ 
angular in shape and measures 2 inches by Vg inch inside, and 2\U inches 
by 1% inches outside. Its width is VI inch. As shown in the side view at 
K, it is a frame with the edges bent up so as to form a deep groove run¬ 
ning around the face of the frame for holding a coil of fine wire. Where 
the frame overlaps it must be neatly soldered. At the corners the turned- 
up edges will be cut away, but this will do no harm. Line the slot in this 
frame with a layer of thin but tough paper, fastened in place by shallac. 
This serves to insulate the frame. Then wind the slot full of No. 36 single 
silk covered magnet wire. 

The ends of this coil are left projecting, one at each end. Shallac the 
outer surface of the coil and set it aside to dry. Now make two little 
pieces shown at E, Fig. 408. They are made by taking a piece of thin cop¬ 
per, 1/4 inch by % inch, and soldering to its center a projecting wire of 
stiff brass, 14 inch long. Flatten the outer end of the brass wire and drill 


330 


TELEPHONOLOGY 


a small hole through the flattened part. These little pieces are then bound 
on to the ends of the coil by silk threads, so that the projecting wires form 
a spindle about which the coil may rotate. For this reason they must be 
so adjusted as to project from the exact centre of each end. Also care 
must be taken, in bending them on, to insulate them from the coils by slip¬ 
ping a piece of thin paper under them. Then the projecting ends of the 
coil are soldered to these little strips, one at each end, and the superfluous 
wire cut off. 

Two pieces of brass should be made like those shown at B, and also 
at H, Fig. 408. As shown in Fig. 407 they are to support the coil in posi¬ 
tion. The hole through B, therefore, should be % inch from the back 
side of the piece, and H should slide freely through B, but may be secured 
by a screw. One of the pieces shown at H should be threaded and pro¬ 
vided with a thumb nut as shown at T, Fig. 407. One end of H should be 
flattened and drilled, as were the ends of the projecting wires on the coil. 
Now procure some fine silk fibers, preferably oi: raw silk, and pass one 
end of the fiber through the hole in the upper wire spindle of the coil, se¬ 
curing it firmly by a drop of sealing wax. In a like manner secure a fiber 
to the lower spindle. Then, with T in place, Fig. 407, pass the fiber 
through the hole in T, pull it up until it is of the right length, and fasten 
with sealing wax. Do the same at the bottom, and the coil will be sus¬ 
pended so as to swing freely in the space between the cylinder and poles. 

Current is led into and out of the coil by two very small slender 
springs shown at the top and bottom. They are made from No. 36 (no 
finer) German silver wire, coiled around a small pencil so as to make a 
very weak spring. By carefully removing T, and leaving the fiber slack, 
the ends of this coil may be soldered to T and to the pivots of the coil. 
This process should be repeated at the bottom. At S is a circular scale, 
made of a piece of white bristol board. It projects forward from the in¬ 
strument, and is bent so as to have the axis of the coil for a centre. The 
radius of the arc of this circle is 2^2 inches. A pointer shown in Fig. 408 
is glued to the bottom of the coil, and its front end moves over the card 
board scale. This pointer is made by taking a strand from a broom, and 
fitting a thin piece of copper at its outer end to serve as an indicator. The 
back end of the pointer projects beyond the coil, and is counter-weighted 
with a small piece of lead, as shown at L. 

Thus the silk fibers serve to suspend the coil in place, so that it may 
swing freely, while the coiled springs encircling the fiber carry the cur¬ 
rent into and out of the coil, and also serve to bring the needle to 0 after 
being deflected. Binding posts at the bottom are connected to the upper 
and lower suspensions as shown. 

If the amateur is skillful he can improve the instrument by using two 
very fine hair springs in place of the coiled German silver springs. These 
may be secured at a watchmaker’s, and besides being more reliable are 
not so stiff as the German silver springs, and therefore render the instru¬ 
ment more sensitive.” 

While the construction of a Wheatstone Bridge is something beyond 
the ability of the average amateur instrument maker, owing to a lack of 
means to properly adjust the various coils, still there are several forms of 
bridges that can be easily constructed, and that are fairly accurate. The 
simplest of these is the so-called “yard stick” slide wire bridge, shown in 
Fig. 409. The American Telephone Journal gives instructions for mak¬ 
ing this instrument, as follows: 


MEASURING INSTRUMENTS AND THEIR USES 


331 


“On some convenient board attach two binding posts B and C. Then 
exactly sixty-two and one-half inches from B and C drive a peg “A”. Af¬ 
ter this is in place stretch a German silver wire of small size, about No. 
19 or No. 22, from B to A to C and attach a receiver to the binding posts 
B and C, thus completing the arrangement of apparatus. To make the 
test, take the pair of wires that is grounded and short circuit them at the 
cable box. The good wire of the pair should then be attached to B, the 
grounded wire to C. Then with the tapper feel along the wire A B until 
you reach a point at which you get no click in your receiver. This will be 
the neutral point of balance. Mark this point and measure its distance 
from A in eighths of an inch. 




You will note that sixty-two and one-half inches equal 500 eighths, so 
you have 500 from A to B and 500 from A to C, making in all a total of 
1,000. Therefore, one thousandth of this, or one eighth of an inch, will 
equal one one-thousandth of the circuit in your cable. If your cable is 
three thousand feet long your circuit would be twice that, or six thousand 
feet, and if one section on your slide wire equals one one-thousandth of 
your circuit, each eighth of an inch would therefore equal six feet. So if 
you find the neutral point of balance to be 120 eighths of an inch from A you 
would have 120 X 6 = 720 feet, the distance of the fault from the cen¬ 
tral office, or having 

L = length of cable in feet, 

S = spaces from A to neutral, 

F = distance from cable box to fault, 
then the formula would be 

L X 2 

- X S = F. 

1000 

The above test shows the instrument as applied to locating cable 
trouble. Of course any other resistance measurements can be made with 

it. 

The Ohmmeter is an instrument often used in telephone work. It is 
a very desirable form of testing set, and has perhaps reached its highest 
development in the lineman’s fault finder, and similar instruments de¬ 
scribed in Chapter IX. 





























332 


TELEPHONOLOGY 


Those who have some mechanical knowledge and a few tools can easi¬ 
ly construct an instrument that will be amply sufficient for a great deal of 
practical work. The ingenious will at once perceive many advantageous 
modifications that can be made from the instrument here described, and 
those who desire can elaborate the instrument to any extent that they 
wish: 

*“The materials required in the construction of an Ohmmeter are 
few. First, there must be a foundation, which may be a piece of carefully 
seasoned, thoroughly varnished pine, or if preferred, the instrument may 
be encased in a suitable box, the bottom of which will serve to support the 
various pieces of apparatus. A resistance wire must be provided. This 
may be procured from any of the well-known instrument makers. 

The best form of resistance wire is that known as Maniganin, which 
can be obtained in almost any of the ordinary sizes, No. 18 wire averaging 
about an ohm to the foot, although the resistance will vary greatly with 
the differences in composition. The actual resistances, however, are not 
of very great importance, so long as the wire is carefully drawn so that it 
is essentially uniform in resistance from end to end. A piece of this wire 
about ten feet in length should be procured. 

Upon the foundation board a paper scale is made which would be di¬ 
vided into say 500 or a thousand parts. This scale may be either drawn 
upon a sheet of Bristol board, or what is still more convenient, a piece of 
cross section paper, may be used and is numbered from 0 to 500. Five 
pieces of the resistance wire are stretched over the scale ao as to form a 
continuous piece about 10 feet in length. At each end the wire is secured 
under some brass plates so that only that portion of the wire which is 
within the limit of the scale enters into the circuit. At one end of the re¬ 
sistance wire a binding post A is attached, which also forms one post to 
which the resistance X to be measured is attached. 

For standard resistances it is best to procure four coils, one of 1 ohm, 
one of 10, one of 100, and one of 1,000. These may be purchased from 
any instrument maker, but it.should be specified that the coils are to be 
wound non-inductively, that is to say that the requisite wire to make up 
the specified resistance is measured off and then doubled in the center. 
The wire is then wound on the spool so that any magnetizing effect is 
avoided. The four point switch must now be provided to which each end 
of the standard coils are connected, when they have been mounted upon 
the foundation board. The necessary apparatus is completed by a re¬ 
ceiver, preferably of the head gear type, which is supplied with two long 
flexible cords, one having a knife edge terminal provided with an insulat¬ 
ing handle to act as a detector. There must also be a small hand genera¬ 
tor as a source of electricity. If preferred, a battery and vibrating coil or 
a battery and a galvanometer may be substituted for the hand generator 
and the receiver. An ordinary battery will not do if a receiver is used, as 
it is best to have an alternating current so that there will be a plainly au¬ 
dible sound in the receiver when there is a state of unbalance in the cir¬ 
cuit. 

In Fig. 410 a simplified diagram of the circuit is shown. From in¬ 
spection of this it is evident that the ohmmeter is simply a modification of 
the ordinary slide-wire bridge. The same system of lettering is carried 
through both the figures, and Fig. 411 is a diagram of the circuits as the 
apparatus is assembled. The heavy full line A B represents the resis- 


*American Telephone Journal. 



MEASURING INSTRUMENTS AND THEIR USES 


333 


tance wire. At the point A a binding post is attached, and from this a 
connection is extended to the generator and connected to one terminal 
thereof. From the other terminal of the generator a connection is taken 
to the resistance wire. Close by the binding post 4 a second similar binding 
post B' is mounted. These binding posts serve to connect the object whose 
resistance is to be measured to the Ohmmeter. To the binding post B' 
one terminal of the receiver R is connected. Also from this point a wire 
is extended to the center post and the four point switch, while to each of 
the other posts one of the ends of the various standard coils are attached, 
as shown in Fig. 410. The other ends of these coils connect to a lead that 
extends from the generator to the B end of the resistance wire. 

An inspection of this drawing will show the circuit to be as follows: 
First, there is a circuit from the generator, through the resistance wire, 
and back to the generator. If the gap X between A and B' is closed by a 
resistance or other object there is a circuit in parallel with the wire A B 
formed from A to B', thence to the switch through either one of the stand¬ 
ard coils to which the switch lever may be connected and thence to the 
generator. 



Fig. 411. 


To use the Ohmmeter, introduce the object to be measured at X be¬ 
tween the binding posts A and B. Place the receiver to the ear, turn the 
crank of the generator, take the free terminal of the receiver which should 
be provided with a metallic knife edge with an insulating handle, and pass 
it to and fro over the resistance wire until a point on the resistance wire 
is found at which the receiver becomes quiet and the throbbing of the gen¬ 
erator cannot be heard. Supposing the scales of the Ohmmeter be con¬ 
structed as shown in the illustration, and as a concrete example assume 
that the switch lever is on the hundred ohm coil, and that the receiver ter¬ 
minal stands at 300 upon the resistance scale, the total length of the scale 
is 500 divisions, the standard coil is 100 ohms, then the following equation 
holds true: 

300 

X = - X 100 = 150 ohms. 

200 















































334 


TELEPHONOLOGY 


In other words, divide the number on the scale opposite which the re¬ 
ceiver contact stands by the difference between this number and the full 
reading of the scale. (In this example the receiver point stopped at 300. 
The whole length of the scale is 500. 500 — 300 = 200 and multiply 

the coil used by this quotient. 

It cannot be expected that an Ohmmeter of this description will have 
the refinements and the extreme accuracy of the more expensive instru¬ 
ments, yet if carefully made it may be expected to be accurate within 1 per 
cent., which is usually near enough for all excepting the most refined in¬ 
vestigations. 

It is desirable to exercise some care in selecting the generator in or¬ 
der to procure a machine which shall be as noiseless as possible, because 
as the point of balance is found by listening to the receiver any external 
noise is liable to interfere with the connection of local points. Under these 
circumstances it is necessary to enclose a generator in a box in order to 
deaden the noise as much as possible. It would not be a good plan to 
mount the generator on the same board with the other apparatus, as k 
will be so noisy as to interfere with the tests. In an exchange where 
there is a power generator a circuit from that can be used. 




Fig. 412. 


If one Cares to go to the extra trouble and expense it is exceedingly 
convenient to wind the resistance wire A B, upon a large circular spool 
and mount it upon a spindle with a contact spring, which takes the place 
of the knife edge) arranged to press against the wire on the spbol instead 
of the separate contact in the receiver cord. By this means a very long 
piece of resistance wire can be used and by counting or providing an in¬ 
dicator to measure the number of revolutions which the wire drum makes, 
very great accuracy can be secured. 

A somewhat more elaborate Ohmmeter may be constructed accord¬ 
ing to the following plan. This instrument was designed to meet the re¬ 
quirements of a large exchange where the repair department had to con¬ 
stantly test the resistance of re-wound ringer coils, etc. The instrument 


















































































MEASURING INSTRUMENTS AND THEIR USES 335 

is very accurate and if properly made will not be subject to inaccuracies 
such as are caused by wear of the sliding contact, etc. 

Fig. 412 shows a plan of the instrument, and a simplified circuit of 
same. The box or case is about 44" long, 16" wide and 4" high. The cov¬ 
er is permanently attached to the box, and projects about all around. 
The box is hinged at the bottom, and the bottom should project about 1 1 / 2 " 
all around. 

A suitable opening is made for the galvanometer, which should be of 
the portable, needle type, of rigid construction and ample sensibility. The 
type of instrument usually used in portable testing sets is suitable. 


n 








t-jr-fc-r-A 

•S' 


7% 





Ji'A/i-*? fir* 

I 1 I 1 • 1 ’ ' 


*"-1 


Fig. 413. 



The resistance coils must be purchased from the makers. Four of 
these are needed, of 1, 10, 100, and 1,000 ohms each. These are secured to 
the brass blocks, a a 1 , Fig. 413, by means of brass rods, as shown. The 
four coils and the blocks to which they are connected, are then bolted to¬ 
gether, as shown in Fig. 413, which gives the dimensions of the various 
parts. The holes between pieces a a 1 , etc., and bar B, are reamed with a 
taper reamer and a substantial brass plug made to fit. It will be noticed 
that one side of all the coils connect to bar C, the other side of coil being 
soldered to the brass pin in the centre of the coil, which connects to piece 
a. By inserting the plug in any hole, that coil is connected between C 
and B. 

This method of construction will be found easier for the average am¬ 
ateur than to attempt to make the contact plates as usually furnished by 
the regular instrument makers, as it is very hard to ream the taper holes, 
when there is an air space between the sides, as is usually the case. 

The bars A, B and C are tapped for screws, so that they can be at¬ 
tached to the top of the box. 

Where this arrangement can not be conveniently made, ordinary 
knife switches or other suitable devices may be used. 

A brass rod %" diameter and 48" long is made to carry the sliding 
contact piece. This rod is shown at a Fig. 412, and the end brackets for 
supporting same are shown at d and e Fig. 412. One centre bracket as 
shown at f, must be made and placed underneath the rod. 

A strip of maple about 3" wide and 2' 5i/ 2 " long should be glued to 
the top of the box, so as to raise the slide wire sufficiently above the top 
to permit the scales to be placed underneath the contact slider. 






























































336 


TELEPHONOLOGY 


The contact slider is shown in detail in Fig. 414. A brass tube a is 
taken and made a running fit on the rod, which should be smoothly finish¬ 
ed. Across this tube is placed a saddle e made of German silver. On top 
of this is secured piece b of brass, which carries contact point f and f l in 
each end. 

The various pieces are assembled as shown in the figure, cl being the 
supporting rod. The contact points f and f 1 should normally be out of con¬ 
tact with the slide wires by about Vs" but should be arranged to make 
firm contact when g and g 1 are depressed. 



Fig. 414. 


This arrangement should slide freely on the rod, over its entire length 
without binding or cutting. 

Two Bristol board scales are securely fastened to the top of the box 
as shown in Fig. 412, and suitable strips of glass should be prepared to 
cover these. The glass can be held in place on three sides by a small 
moulding, and on the side nearest the wire by fitting same into a groove 

in the maple strip supporting the slide wires. Have the glass fit tightly so 
that dust cannot penetrate to the scales. 

The slide wire is 17 or 18 guage Maniganin or German silver. Stretch 
the wires tightly across the strip, in which two grooves have been scratch¬ 
ed to more firmly hold the wire, and prevent it moving sideways. Perma¬ 
nently fasten the wire at both ends under screws, see that it is perfectly 
tight, and then shallac the wire into the grooves. 

Two keys are provided for the battery and galvanometer circuits. 
These are marked B and G in the figure, and are of the lever type with 
positive contacts. Posts are provided as shown, for the battery wires. 

Use not less than No. 12 wire to connect the various parts, and re¬ 
member that the resistance must be kept as low as possible, so that no 
error will be introduced in the readings of the apparatus. 























































MEASURING INSTRUMENTS AND THEIR USES 


337 


This bridge may be used same as the one previously described, by 
dividing the scales into 1,000 even parts, but a much more desirable meth¬ 
od, and one that permits of marking the scale so that the result is read 
directly in ohms without any calculation, is to connect a standard resis¬ 
tance box to the X posts, and calibrate the bridge by means of same. To 
do this proceed as follows: 

Connect a battery to the Bat. posts; this should be a storage cell, or 
some other source of current that will not weaken or change during the 
test. In a common battery office, it can be the exchange battery in series 
with a fixed resistance of 50 ohms. Connect the resistance box to the X 
posts and implug a certain resistance—say 10 ohms. Now put in one of 
the standard coil plugs—say the 100 ohm plug, and slide the contact 
along the wires, meanwhile tapping the keys, until a balance is found, and 
the galvanometer ceases to move from the centre or zero point. Mark this 
place on the scale, in this case it is 10 ohms. Now implug 11 ohms and 
proceed as before; it will be found that the contact need only be moved a 
short space to find this point. Continue in this manner until the scales 
have been marked throughout their length. 

It will be found that the divisions will be close together at some 
points and further apart at others, this should not cause any uneasiness 
if the galvanometer is watched closely and an absolute balance secured for 
each reading. 

Do not let the wires get too warm, which will occur if the battery key 
is kept constantly depressed. It is better to just tap the battery key. 

It is best to use the standard coil nearest the actual resistances the set 
is being constructed to measure. Calibrate the scales using this coil only, 
throughout their entire length. If the 100 ohm coil is used, upon chang¬ 
ing to the 1,000 ohm coil, the readings will be increased by 10, or if the 10 
ohm coil is used the readings will be decreased by 10, and if the 1 ohm 
coil, by 100. 

To illustrate this, suppose the 100 ohm coil is used, and 10 ohms is 
unplugged in the resistance box, and a point on the scale is located where 
the galvanometer needle no longer moves; this is marked 10, meaning 10 
ohms. 

Now change to the 1,000 ohm coil, and it will be found necessary to 
unplug 100 ohms in the resistance box before the galvanometer will bal¬ 
ance at the same point on the scale. 

By using the 10 ohm coil, the point that was 10 ohms with the 100 
ohm coil, becomes 1 ohm, and by using the 1 ohm coil, it becomes .1 ohm. 

It is very easy to calibrate the bridge by using the 100 ohm. coil, and 
then adding an 0 to each figure. When using the 1,000 ohm coil the fig¬ 
ures are increased in value by this cipher, thus 10 reading 100, 50 reading 
500, and so on. Or the value is decreased if the 10 ohm coil is used, thus 
10 becomes 1, 50 becomes 5, and so on. 

The complete instrument is shown in Fig. 414a. If carefully made 
and calibrated it is very accurate, this depending upon the accuracy of tie 
resistance box used, and the accuracy of the relative resistance of the 
standard coils used in the bridge. 

The bridge is of course more accurate for readings made using the 
same coil as used when calibrating the bridge. A slight inaccuracy may 
be noticed when the other coils are used; to test this proceed as follows. 


22 


338 


TELEPHONOLOGY 


Use 100 ohm coil, implug 100 ohms in resistance box, note balance 
point on scale and mark this 100. 

Change to 1,000 ohm coil, unplug 1,000 ohms in resistance box, and 
balance should be same as before. 

Change to 10 ohm coil, inplug 10 ohms, balance should be same as be¬ 
fore. 

As the instrument is direct reading it is very convenient where a 
large number of measurements are constantly being made. 

Change to 1 ohm coil, unplug 1 ohm, balance should be same as before. 

Every exchange should be equipped with a voltmeter, and this is 
usually mounted upon a desk type switchboard, and is usually termed a 
“test table” or wire chief’s desk. 

A simple arrangement of this character may consist of an ordinary 
telephone equipped with a volt-meter of the type shown in Fig. 379. Any 
bridging telephone may be used, the voltmeter being mounted on the door 
where the bells are usually placed. Two double throw keys are necessary, 
wired as shown in Fig. 415. While the complete phone wiring is shown, 
it will be understood that this exact wiring need not be adhered to, as any 
standard bridging phone may be used, provided the keys and voltmeter 
are connected as shown. 



Fig. 414a. Complete Ohmmeter. 


When No. 1 key is thrown to the left, thereby operating the thrown 
side marked A the batteries are connected directly to the voltmeter, and 
when th^pwn to the right side B is operated, the battery, voltmeter and 
line are in series, and the resistance of the line, short circuits, etc., can be 
measured in the usual manner. 

To test for a ground on the side o" the line marked L in the figure 
throw Key No. 1 to B and Key No. 2 to B, this will ground line 2, and 
thereby show the leakage from line 1 to line 2 or ground. 

Throwing Key 2 to A will reverse the process, and ground line 1. 

Ordinary ringing and talking tests are made in the usual manner. 

In large exchanges it is customary to furnish a much more elaborate 
equipment, and to supply the wire chief with a small switchboard equip¬ 
ped with various testing applicances adapted to rapidly locate both line 
and equipment troubles. 

The circuits of a standard wire chief’s desk, as furnished by the Wes¬ 
ton Electric Co., are shown in Fig. 417. This equipment is especially de¬ 
signed for use with the standard common battery switchboard equipment 
furnished by this company. J? 

A three conductor plug is used, the sleeve of which is connected to a 
180 ohm resistance coil, so that when this plug is placed in any jack, the 




MEASURING INSTRUMENTS AND THEIR USES 339 

cut off relay or restoring coil, if it is a line ending in a battery restored 
drop, will be operated. 

Keys 1, 2, 3, 4 and 5 are ringing keys. No. 1 connecting ± current 
to the ring of the plug and grounding the sleeve for ringing ordinary 
bells and keys 2, 3, 4 and 5 connecting to -f- and — current for pulsating 
party line ringing. Key D also forms part of the ringing combination, 
as by means of this key 100 or 660 ohm resistance lamps are inserted in 



the ringing circuit, thereby enabling the bells to be adjusted to ring prop¬ 
erly through these resistances, which represent the resistances inserted 
in the ringing leads of the local and trunk operators’ positions at the main 
switchboard. 

Key 6 is an ordinary listening key which connects the wire chief’s 
talking set to the test plug, through the repeating coil, which supplies bat- 



Fig. 417. 

tery to the line under test, same as an ordinary cord circuit. Key A cuts 
off the battery, and connects the test plug directly to the secondary cir¬ 
cuit of the wire chief’s talking set, thus making the circuit same as a mag¬ 
neto line, by removing the battery from the line under test. 


























































































































































































340 


TELEPHONOLOGY 


Key C accomplishes the same result but puts the repeating coil in cir¬ 
cuit between the wire chiefs’ talking set and the line under test. 

Key B when thrown, grounds one side of the receiver, to enable list¬ 
ening tests to be made from line to ground. 

The wiring of the wire chief’s talking set is practically the same as 
that of a operator’s set at a common battery switchboard. The transmit¬ 
ter is in series with a 165 ohm impedance coil and the 17 ohm primary of 
an induction coil. The secondary circuit consists of the receiver and sec¬ 
ondary of coil in series, with a 2 M. F. condenser and the line. The opera¬ 
tion of this circuit is fully described in connection with common battery 
switchboard. 

Key 7 is a reversing key, whereby the ground side or , the circuit 
which is normally ori the tip of the plug, is changed to the ring and the 
battery side of the circuit applied to the tip. 



Fig. 418. 



Key 8 when thrown, grounds the ring side of the cord circuit. By 
tracing the circuit from battery, it will be seen that the voltmeter is nor¬ 
mally in series with the ring side of the circuit, and that the tip side is 
open at Key 6. Now by throwing Key 9, if a ground exists on the ring side 
of the line, the voltmeter will immediately indicate this, but if the circuit 
is 0. K. or the ground is on the tip side of the line under test, it will be 
necessary to throw Key 8 before the circuit is completed. 

If the ground is on the tip side, it can be located by throwing Key 7. 

Key 10 disconnects everything from the test circuit except the volt¬ 
meter, which is bridged directly across the cord. Throwing Key 8 will 
then ground the tip side of the voltmeter and cord circuit, and by Key 7 
the ground may be reversed. 


























MEASURING INSTRUMENTS AND THEIR USES 


341 


Key 11 places the milli-ammeter in circuit same as Key 9 did the 
voltmeter. A 100 ohm resistance coil is in series with the ammeter to 
protect it from damage in case of a dead short circuit on the test line. This 
resistance should be subtracted from the result when making resistance 
calculations. Key 12 short circuits this coil, where it is necessary to re¬ 
move same from the circuit in order to obtain sufficient deflection. The 
ammeter usually has a range of 300 milli-amperes. 

Key 13 places the 125 ohm sounder in series with the ring side of the 
circuit in series with a 300 ohm resistance coil, used to prevent an execes- 
sive flow of current. The sounder is very handy for making tests as it 
can be, for instance, be left connected to a line upon which work is being 
done, and when the trouble man calls in, the sounder will call attention to 
the fact, if the wire chiei is busy in some other part of the room. 

Experience is necessary to become proficient in quickly making tests 
with this equipment, but the layout here given is the result of much prac¬ 
tical experience and experiment with a view to simplifying the circuit as 
much as possible. 



Fig. 419. 


The general appearance of a wire chief’s desk is shown in Fig. 418. 

The ammeter and voltmeter are usually of the Weston make. The 
location of the apparatus is plainly shown in the illustration. 

A circuit differing in detail from the one just described, is shown in 
Fig. 419. This is arranged to work in connection with the common battery 
equipment furnished by one of the large manufacturers. The American 
Telephone Journal describes the operation of the keys as follows: 

“The wire chief’s board is provided with jacks connected to plugs 
terminating on the multiple board which are inserted by operators in case 
of trouble appearing in the jacks of line in trouble and still other jacks 
are provided for testing trunks to the main distributing frame. 

The plug shown in Fig. 419 is inserted in the jack of the cord con¬ 
nected to the line to be tested, and by the proper manipulation of the keys 
shown, any of the customary tests may be made. 

Key No. 1 is a ringing key which allows the wire chief to ring out on 
the line, thus determining whether the subscriber can be laised or not. 








































































































































342 


TELEPHONOLOGY 


Key No. 2 is the reversing key which reverses the entire testing 
equipment with respect to the tip and the ringing sides of the line being 
tested. 

Keys Nos. 3 and 4 are for grounding the different sides of the line. 
Key No. 3 grounding the ring side and No. 4 the tip side. 

Key No. 5 is the voltmeter key which when operated together with 
Key No. 1, bridges the volt-meter on to the line for making the desired 
tests. 

Key No. 6 is the relay key and is connected, as you will note, in such 
a manner as to operate the 60-ohm relay when there is a ground on the 
line, thus causing the ground signalling bell to be actuated. This is a test 
for ground on either side of the line, as the line may be reversed by the ac¬ 
tuation of key No. 2 by the wire chief. 

Key No. 7 is a continuous ringing key; that is, a key to which the 
leads of a continuous ringing generator are connected. This may be used 
in place of key No. 1 in signaling the instrument desired. 

Key No. 8 is left spare in order to provide for any future contin¬ 
gencies. 

Key. No. 9 connects the cord circuit to the wire chief’s talking set so 
that conversation may be had upon the line. The inner contacts of this 
key are connected to other listening keys where more than one wire chief’s 
ppsition is installed, and may be left unoccupied where but one position is 
used. 

Key No. 10 bridges the retardation coil across the line so that when 
the wirechief is talking to some person through the board, by throwing 
the retardation coil key, the supervisory signal in front of the operator is 
extinguished, thus allowing the wire chief, by throwing the listening key 
No. 9, to carry on any conversation he may desire, and bv returning key 
No. 10 to its normal position the supervisory signal will light, thus advis- 
iiig the operator that the use of the line is no longer required and that the 
connection may be taken down. 

Key No. 11 is for the purpose of connecting battery cord circuits 
through repeating coil or retardation coil for any particular purpose that 
may be desired where the full force of the battery is not required. 

Key No. 12 cuts off the battery from the voltmeter. Where quick 
readings are desired, this key may be operated rapidly. 

Key No. 13 is for connecting the six volt battery to the low scale of 
the voltmeter. 

Key No. 14 is for connecting the shunt across the low reading scale of 
the voltmeter in order that by comparison of this winding with the total 
resistance of the voltmeter circuit and by the application of the voltmeter 
shunt principle of measuring, an increased reading may be obtained on the 
voltmeter where the trouble is of such a nature that a sufficiently large 
deflection for easy reading would not be obtained where the force of the 
battery was flowing through the voltmeter, the line and the trouble, in 
series. 

In this circuit a voltmeter has been employed for the purpose of mak¬ 
ing the measurements, as with this instrument the necessary tests can be 
performed more readily and with greater degree of exactness in a given 
time than by other means. Sometimes a Wheatstone Bridge is substituted, 
and so arranged that it may be conveniently and rapidly connected to or 


MEASURING INSTRUMENTS AND THEIR USES 


343 


disconnected from any line on which the wire chief may be desirous of 
making a test.” 

The 6 and 120 volt batteries may consist of ordinary dry cells. 

There are several other circuits used in connection with the wire 
chief’s testing equipment, but as it is only intended to refer to the arrange¬ 
ment and use of the instruments used, at this time, a description of these 
circuits will be given later. 

Portable test sets for linemen’s use, consist of a telephone instrument 
compactly arranged so as to be easily transported. A set for use on mag¬ 
neto systems is shown in Fig. 419a. It consists of a magneto buzzer and 
2 bar generator in series, and a special receiver. A switch is arranged to 
cut the receiver in and out of circuit. 


Fig. 419a. 

A regular transmitter and batteries are sometimes furnished, ana the 
generator may be equipped to give pulsating current so that central may 
be called without ringing the phone bell on the line. 

In common battery systems the generator is unnecessary, and it is 
customary to furnish the trouble man with a transmitter and receiver in 
series, and contained in one handle, as shown in Fig. 419b. The cord is 
equipped with snap clips, to facilitate attaching the set to the line wires. 




Fig. 419b. 

On common battery work, it is possible to use an ordinary head 
receiver, using it as transmitter and receiver. If it does not transmi 
well when first connected to t^e lire, reverse the connection, so the line 
battery will flow through it in the proper manner. 





CHAPTER XI. 


COMMON BATTERY EQUIPMENT. 


The main difference between magneto and common battery systems 
is that with the common battery system; ,the central office is signaled by 
merely removing the receiver from the hook, while with the magneto sys¬ 
tem it is necessary to turn the generator crank. Upon finishing the con¬ 
versation, it is not necessary to ring off, as this is automatically perform¬ 
ed by replacing the receiver on the hook. 

From this it is evident that there must be a current on the line wires 
all the time so that when the receiver is taken off the circuit is closed and 
the operator at the central office is thereby notified that a conversation is 
desired. j 



With the common battery system a different class of signals may bo 
employed from those used in magneto work. The usual drop or signal 
used in magneto work has a shutter which is restored by hand, or by in¬ 
serting the plug in the jack, and so designed that when the shutter falls 
after receiving the first impulse from the generator, it remains displayed 
until restored by the operator. This is necessary or the subscriber would 
have to continually turn the generator to display the signal until the ope¬ 
rator answered. In common battery systems the signal is displayed as 
long as the receiver is off the hook. 

Two types of common battery signals are in common use. One is the 
so called visual signal which consists of a drop with the shutter so attach¬ 
ed that it is displayed when a current passes through the coil. 

Another type of signal that is used extensively in larger exchanges 
is a miniature incandescent lamp mounted back of a small glass cap. The 
lamp is lighted by the operation of a relay, which will be described later. 

Fig. 420 shows the arrangement for signalling when a visual type 
of signal is used. The battery may be from 20 to 48 volts, and the signal 
may have a resistance of 80 to 500 ohms. When the circuit is closed by 
the removal of the receiver from the hook, current will flow from the bat¬ 
tery, over the tip line, through the transmitter and receiver and through 
the sleeve side of the line and the visual signal winding C, to the battery. 

(344) 
























COMMON BATTERY EQUIPMENT 


345 


This causes the armature of the visual to be attracted, and the shutter 
S is displayed. When the plug is inserted in the jack, the circuit through 
the signal is broken, and the shutter is no longer held in the exposed posi¬ 
tion. 



Fig. 421. 


A strip of visual signals as furnished by the North Electric Co. are 
shown in Fig. 421. When in the normal position the shutters are hidden 
by the front plates, but when the visuals are actuated the shutters are 
displayed through the slots, as shown in the figure. 



Western Electric Visual. 


Fig. 422 shows the circuit when lamps are used. Here a relay, R is 
placed in the circuit, the lamp being controlled by the contacts of this re¬ 
lay. It is obviously impossible to include the lamp directly in the line cir- 



Monarch Tel. Mfg. Co., Visual. 


cuit, as if sufficient battery was used to light the lamp through the resis¬ 
tance of a long line, it would burn up on a short line. By using the relay, 
the lamp is always subm^ed to the same current, as the resistance of the 
lamp circuit is not variable. 




346 


TELEPHONOLOGY 


It may be stated that Figs. 420 and 422 show in theory only, the vis¬ 
ual and lamp signal methods of operation. Both of the circuits shown are 
only suitable for small boards, and other equipment is necessary in con¬ 
nection with common battery calling circuits, especially in large boards. 
These figures however, show that the exchange may be signalled with the 
common battery system, by simply removing the receiver from the hook 
thereby completing the circuit through the signal apparatus at the switch¬ 
board. v 

One difficulty encountered in this system is the fact that while the 
circuit at the telephone must be kept open when the phone is not in use, 
the ringer must be connected to the line so that Central can call the phone. 
This was accomplished by winding the ringer to a resistance of several 
thousand ohms, and bridging it on the line, as shown in Fig. 423 and ad¬ 
justing the line signal so that it would not operate through the high resis¬ 
tance ringer but would operate when a low resistance path was afforded 
through the receiver and transmitter. This method proved very unsatis¬ 
factory for the reason that a small but constant leakage of current occur¬ 
red through the ringer, and in an exchange of several hundred lines, this 
leak became large enough to be serious. 



The constant flow of current through the polarized ringer, also had 
a weakening effect on the magnet. The signal or relay also required fre¬ 
quent adjustment, as it would “stick” after having been pulled up, by rea¬ 
son of the small current passing through the coil. These troubles caused 
this method to be abandoned. 

Another scheme was to connect the ringer from one line to ground, as 
shown in Fig. 424. While this removed the objection of the current al¬ 
ways flowing through the ringer, it is objectionable to use the ground for 
ringing and for this and other reasons this method was abandoned. 

The standard and now universally used method of arranging the 
ringer circuit, is to place a condenser in series with the ringer, as shown 
in Fig. 425. The condenser is the same as an open circuit to the direct 
current and no current passes, while to the ringing current which is al¬ 
ternating, it offers but little opposition, consequently the ringer is operat¬ 
ed. The usual arrangement is to use a 1,000 ohm ringer and 2 M. F. con¬ 
denser, this always being the case where the condenser forms part of the 
talking circuit, otherwise a 1 M. F. condenser and 500 ohm ringer may be 
used. In the following circuit diagrams it will be understood that a ring¬ 
er and condenser forms part of the circuit. These are sometimes omitted 
for the sake of clearness. 

From the foregoing it will be understood how the phone may call the 
Central office, and be called. It is also apparent that where there is more 
than one phone on a line, that the phones cannot call each other, as Central 



































COMMON BATTERY EQUIPMENT 347 


must do all the ringing. This is the case except in some special cases 
as described later. 

The generators are of course eliminated from common battery in¬ 
struments, and also the batteries, the transmitters being supplied from a 
battery at the Central office, this usually being the same battery that is 
used for operating the line signals. 

Fig. 426 shows one method of supplying battery to the transmitters. 
The battery is placed in the cord circuit as shown. A separate battery 
for each cord circuit may be used or, if the battery is of very low internal 
resistance, such as a storage battery, all the cord circuits may be con¬ 
nected to the same battery, as shown in Fig. 427. Under these circum¬ 
stances conversation is possible between phones connected by plugs A and 
B, while phones C and D connected to the second cord circuit are also talk¬ 
ing. While only two cord circuits are shown in the figure, it should be 
remembered that any number could be connected to the battery. 

Phones connected by C and D can talk owing to the low resistance of 
the battery at points X and Y, (these usually consisting of heavy copper 
buss bars) and very little cross talk fromi A and B will result. This is the 
principle of the method of supplying talking battery, in the comon bat¬ 
tery system. 


♦ 






The circuit shown in Fig. 427 has some serious faults; one is that 
unless the buss bars and battery are of very low resistance cross talk will 
result. 

Fig. 428 shows a partial remedy for cross talk. The impedance coils 
I P are inserted between the battery and the sleeve side of each cord cir¬ 
cuit. It will now be seen that while the impedance coils will permit suf¬ 
ficient direct current to flow out to each cord circuit to supply the trans¬ 
mitters, the impedance of the coils will prevent the voice currents from 
being short circuited by, or from flowing into the battery, and they flow 
directly from telephone to telephone. This arrangement successfully pre¬ 
vents cross talk, as voice currents from one cord cannot affect another, 
owing to the impedance coils. 

It is evident that if the line connected to plug A, Fig. 428, is of less 
resistance than the line connected to plug B, that most of the current will 
flow over the A line, and the B line will not get enough battery to properly 
operate the transmitter. This is remedied by using the arrangement 
shown in Fig. 429, which is the method usually used by the Bell Com¬ 
panies. 
































348 


TELEPHONOLOGY 


A Repeating coil is used, with 4 windings, all wound on the same 

core. 

Windings 1 and 2 form one half of the coil, 3 and 4 the other. As the 
current for each line flows over the windings connected to that line only, 
the resistance of one line can in no way effect the current supply of the 
other. The voice currents from line A are repeated from windings 1 and 
2 of the coil, to line B through windings 3 and 4, but any stray currents 
from other cord circuits which may present at points X and Y, are pre¬ 
vented from getting into the cord circuit by the impedance of the coil, 
which acts same as an impedance coil in respect to any alternating cur¬ 
rent that may attempt to flow into the cord circuit from points X and Y. 

There are several other methods of supplying the battery to the trans¬ 
mitters and these are described in connection with complete switchboard 
circuits. 




Fig. 430. 

So far, the circuit arrangement of the subscriber’s telephone has not 
been considered, and for the sake of clearness the transmitter and receiv¬ 
er have been shown in some of the drawings connected in series. This ar¬ 
rangement is shown in Fig. 430. Here the receiver and transmitter are 
in series so that the entire direct current flowing from the central office, 
used for signalling purposes as well as for transmitting, passes through 
the receiver coils. 

Unless the receiver is connected so that this steady flow of current in¬ 
creases rather than diminishes the efficiency of its magnet, a serious loss 
in efficiency results. It is at once apparent that this type of circuit is not 
practical for ordinary exchange work, as the accidental reversal of the 
line conductors at the distributing frame or at a manhole or pole, will 
cause a reversal of current through the receiver and a consequent weak¬ 
ening of the magnet, and the receiver is not in a condition to give its maxi¬ 
mum sufficiency. 

































COMMON BATTERY EQUIPMENT 


349 


An increase in the magnetism due to battery flowing through the 
coils in the proper direction, is often sufficient to pull the diaphragm into 
such close proximity to the pole pieces that its vibration is interfered 
with. For these reasons this circuit is used to a very limited extent, 
usually only in private telephone installations where the line wires re¬ 
main constant in their resistance and are not as subject to reversal as the 
wires of outside plants. In attempting to secure the best results and yet 
prevent the flow of current through the receiver so as to give it unhinder¬ 
ed action, a variety of means have been tried. Fig. 431 shows one circuit 
in common use. 

Here the receiver is placed in a local circuit formed by one winding 
of the induction coil, while the transmitter and hook contacts are placed 
in circuit with the other winding. The strait single headed arrows show 




LINS: •&> 


TRANSMITTER. 


INDUCTION COII_j 




RECEIVER. 



Fig. 431. 

the path taken by the direct current, while those with double heads repre¬ 
sent the voice currents. The incoming voice currents are induced rom 
one winding of the coil to the other. The coil commonly used in connec¬ 
tion with this set is of the following dimensions, the core consisting ot 
No. 26 iron wire 7-16" in diameter and 4V«" long. Heads 1 Vs" square, 
5-16" thick. Space between heads, 3 1 /?"- Two layers of paper are placed 
over the core. The first winding consists of 1450 turns of No. 26 single 
silk covered wire put on in 8 layers of 180 turns each. One piece ot thin 
paper is placed between each layer. This winding is wound from left to 
right, the coil is then turned over, and two layers of thin paper are placed 
over the first winding. The outside winding is then put on, which con¬ 
sists of 1062 turns of No. 26 single silk covered wire, put on in 6 layers ot 
about 180 turns each, with a piece of pap Q r between each layer. The tei- 
minals are brought out and numbered as follows: 

Inside end of inside winding. ^°* 

Outside end of inside winding. {j 0. 

Inside end of outside winding. g: 0. 

Outside end of outside winding. ^°* 


2 . 

3. 

4. 







































350 


TELE PHONOLOGY 


Terminals, No. 1 and 2 connect to the receiver, No. 3 to the line, and 
No. 4 to the transmitter. The resistance of each coil should be about 
10 1/2 ohms. Another coil of smaller dimensions with a winding space of 
2 V 2 “inches, head li/ 8 by % thick, with a core % inches in diameter, has an 
inside winding of 1320 turns of No. 26 single silk wire 8i/ 2 layers, with 
outside winding of 1320 turns No. 26 put on in 10i/ 2 layers, each winding 
having a resistance of IOV2 ohms. The receiver used with this instrument 
is usually wound to a resistance of 25 ohms. 

This circuit arrangement transmits very well, but it is slightly de¬ 
ficient in receiving qualities, as the voice currents reach the receiver en¬ 
tirely by the inductive effect of the coil, the receiver having no actual con¬ 
nection with the line wires whatever. 



Fig. 432. Fig. 433. Fig. 434. Fig. 435. Fig. 436. Fig. 437. 


The circuit arrangement usually employed by the Bell Companies is 
shown in Fig. 432. The dimensions for the standard induction coil being 
as follows: Core of 24 iron wire 7-16" in diameter, and 414 ," long. Heads 
1%" square and %" thick. Winding space 31 / 2 ". Enough paper is wound 
over core to make same 1 / 2 " in diameter. The inside winding consists of 
about 1400 turns of No. 31 single cotton covered wire, put on in six layers. 
Resistance from 26 to 30 ohms. Two layers of paper are put on and then 
without removing the coil from the winding machine, the outside wind¬ 
ing which consists of 1700 turns of No. 26 cotton wire, resistance from 
15.5 to 17 ohms, is wound on. The terminals are numbered as follows: 


Inside end of outside winding. No. 1. 

Outside end of outside winding. No. 2. 

Outside end of inside winding. No. 3. 

Inside end of inside winding. No. 4. 


Connect for circuit shown in Fig. 432 1 to Line: 2 to hook: 3 to con¬ 
denser, 4 to receiver. 

The receiver usually used, is wound to 60 ohms, with 34 single silk 
covered wire. 

When the transmitter is sensitive, and the circuit, Fig. 432 is used, 
the “side tone” may be objectionable, and to overcome this the arrange¬ 
ment shown in Fig. 433 may be used, with a 75 or 80 ohm receiver. 

In Figs. 434, 435, 436 and 437 are shown some arrangements that 
can be used with this circuit, none of which excel that shown in Fig. 432. 

Referring to the coil used in this type, when arranged as shown in 
Fig. 432, and considering terminals 1 and 2 as the primary, and 3 and 4 as 
the secondary, if the pri. and sec. are reversed, transmission will be de¬ 
creased about 50%. 







































COMMON BATTERY EQUIPMENT 


351 


If it is thought that terminals 1 and 2 or 3 and 4 are reversed, short 
circuit the condenser and if the coil is O. K., the core of the coil will be¬ 
come magnetized more strongly. If not O. K., the magnetism will de¬ 
crease; this can be ascertained by holding a nail or other light piece of 
iron near the core while short circuiting the condenser. 

If 1 and 3 are reversed the telephone will have very little side tone. 
The instrument may talk fairly well as the transmitter and receiver will 
be in series. Test for this by reversing the line wires, whereupon the pull 
of the receiver magnets on the diaphragm will be noticeably weakened. If 
2 and 4 are reversed, the effect will be the same. 

Mr. M. Blight, in The National Telephone Journal, clearly describes 
the operation of this coil as follows: 

“The incoming speech currents pass from the “-j-” line through the 
15-ohm winding of the induction coil, and then divide, a portion going 
through the transmitter, and a portion through the receiver, 30-ohm 
winding of coil and condenser (see Fig. 438.) The currents which thus 
reach the receiver direct are so small as to be practically negligible, owing 
to the existence of the much easier non-inductive path offered by the 
transmitter. The currents that really affect the receiver are induced in 
the 30-ohm winding of the coil by the passage of the currents in the 15- 
ohm winding and circulate in the circuit in the direction indicated by the 
dotted arrows. The slight direct effect, it will be noticed, is in the oppo¬ 
site direction to that of the induced currents. 



Fig. 438. 



Transmitting .—The transmitter acts in two distinctly different 
ways; first, by varying the resistance of the line circuit, it directly varies 
the current flowing out through the repeating coil at the exchange, and 
secondly, by effects induced in the 15-ohm winding of the induction coil, 
it controls the variation of the line current. To make the operation clear, 
consider the transmitter diaphragm is moving outwards and its resistance 
consequently increasing (see Fig. 439). The current flowing in the line 
in the direction o e the arrows is then decreasing. The condenser is nor¬ 
mally charged by the potential difference existing at the transmitter ter¬ 
minals. When, with an increase in the transmitter resistance, this po¬ 
tential difference increases, a current flows into the condenser, passing 
through the 30-ohm winding of the coil in the direction of the arrow. 
Thus is there induced in the 15-ohm winding an electro-motive force in the 
direction of the dotted arrow, and this it will be noticed, is opposing the 
line current and consequently diminishing it. The direct and induced ef¬ 
fects of the transmitter thus both assist in the reduction of the line cur¬ 
rent. 












































352 


TELEPHONOLOGY 


When the transmitter diaphragm recedes the reverse takes place 
(see Fig. 440). The line current is strengthened by the induced effect. 
The falling potential difference across the transmitter terminals causes 
the condenser to discharge proportionately and a current flows through 
the 30-ohm winding in the direction of the arrow. This induces an elec¬ 
tro-motive force in the 15-ohm winding in the direction of the dotted ar¬ 
row, which assists the line current and thus further increases it. 

Note .—To make the matter clearer, in the above sketches the two 
windings of the induction coil are shown one behind the other. Actually 
they are wound in the usual way, one over the other. 

This explanation should enable those concerned to deal with any 
faults that may occur on these instruments. Two faults may be mention¬ 
ed, one at least of which has a rather unexpected result: a high resistance 
in the transmitter circuit will have a detrimental effect upon the receiv¬ 
ing; and the reversal of one winding of the induction coil in relation to 
the other will greatly diminish the transmission, but will not sensibly af¬ 
fect the receiving.” 



Fig. 441 


Fig. 441 shows a circuit in which a departure has been made from 
previous forms. Here it will be seen that the condenser is in series with 
the receiver, the incoming direct currents are therefore barred, as the 
condenser will not allow the passage of direct current. The transmitter 
is arranged in series with a retardation coil, the dimensions of which are 
as folllows: 

Heads: 1" square, Core 14 " in diameter, 3%" long, Winding space 
2%” wound to to resistance of 25 ohms, with No. 28 single silk covered 
wire. 

Owing to the high impedance of this coil the voice currents will not 
pass through it and are therefore, forced through the condenser and re¬ 
ceiver. It is possible to use a high wound receiver as it is removed from 
the transmitting circuit, and this circuit has been found very satisfactory. 















































COMMON BATTERY EQUIPMENT 353 

It is possible to make a coil same as the above of only a few ohms re¬ 
sistance, with the same impedance. When this is done, the condenser 
may be omitted from the receiver circuit, the receiver being connected to 
the terminals of the coil. The only direct current that will pass through 
receiver would be that due to the drop in voltage existing across the ter¬ 
minals of the coil. This arrangement is seldom used. 

The Balanced Bridge Coil, represents another type of circuit. This 
is shown in Fig 442, and employes the principle of the balanced Wheat¬ 
stone bridge to keep the direct current flow from the receiver, while the 
voice currents which are alternating in effect are forced by a combination 
of retardation and low resistance, located in the arms of the bridge, 
through the receiver. 


T LIA& ^ 


TRANSMITTER. 



BALANCED BRIDGE- 
COIl- 




Fig. 442. 

Fig. 443 shows a simplified diagram of this circuit in which A and 
D are retardation coil windings, and B and C non-inductive resistance 
windings. The bridge is balanced for the direct current flow indicated 
by the single headed arrows, by making the ohmic resistance of the four 
arms such that the Wheatstone’s bridge equation, A:B::C:D is balanced. 
There will then be no direct current flow between the points 2 and 3. as 
^heir potential is the same, and the receiver, which takes the place of the 
galvanometer in the regular testing bridge, will be free from direct cur¬ 
rent action. The bridge, however, is out of balance for voice currents, 
which cannot penetrate the high retardations A and D, and are thus 
forced through the receiver and non-inductive resistance A and C in the 
path indicated by the double headed arrows. In practice all of the coils 
of this bridge are wound on one spool and internally connected so that as 
far as external appearances or connections are concerned, it resembles a 
standard induction coil, as shown. The resistance of the four windings 
are approximately 20 ohms each for A and B, and 30 ohms each for C and 
D. The total resistance of the non-inductive windings B and C, which are 
in series with the receiver, is therefore only 50 ohms, thus offering no ap- 































354 


TELEPHONOLOGY 


preciable obstacle to the voice currents, the receiver being practically in 
the line circuit direct, and in a position to receive the maximum available 
incoming transmission with no distortion or losses. 

While it is not necessary for this bridge coil to be absolutely balanced 
for the best transmission, it is found convenient to make this adjustment 
very accurately by the means shown in Fig. 444. After the four coils are 
wound on the spool and tested separately they are soldered to the termi¬ 
nals 1, 2, 3 and 4; the non-inductive winding C being le t purposely slight¬ 
ly of greater resistance than necessary so as to allow for taking up of the 
inequalities of manufacturing. At this stage the coil is inserted in the 
circuit of the special testing set illustrated, with a 24 volt battery connect¬ 
ed to the terminals 1 and 4 and with a very sensitive galvanometer be¬ 
tween terminals 2 and 3. The insulation of the adjacent wires of the non- 
inductive winding C is then scraped back from the loop end E until a 
point is reached where the short circuited wires bring the needle of the 



galvanometer to zero, thereby indicating that no direct current is flowing 
through the bridge 2-3. The wires are then soldered at this point and the 
bridge is thus given a permanent balance. In actual practice the condi¬ 
tions are less severe than in this test, as the galvanometer is replaced by 
the telephone receiver and the flow of battery current in the external cir¬ 
cuit is reduced to less than one-tenth of an ampere by the combined resis¬ 
tance of the switchboard retardation coils, the line and the telephone 
transmitter. : :v,. 

The transmitter receives its current from the line circuit through the 
two 50-ohm halves of the bridge as indicated by the single headed arrows, 
then through the transmitter, the joint resistance of these paths being 25 
ohms, so that the transmitter obtains the full amount of current for 
which it is designed. 

Side tone is greatly reduced which is an important advantage in long 
distance conversation, as the subscriber can hold the receiver tightly to 
the ear while talking, without the deafening effect usually produced. 

One advantage that this circuit would seem to possess is the fact that 
the use of the condenser in the receiver circuit is obviated. As the con- 































COMMON BATTERY EQUIPMENT 


355 


denser offers a resistance to the voice currents in proportion to its electro¬ 
static capacity—about 325 ohms for a 2 M. F. condenser, and 650 ohms 
for a 1 M. F. condenser. 

A circuit based upon the use of a receiver designed so it will not be 
demagnetized by direct current, although placed directly in the line cir¬ 
cuit, consists of this special receiver and a transmitter in series, as pre¬ 
viously shown in Fig. 430. The novel features lie in the design of the re¬ 
ceiver, which is shown in Fig. 445. 

*“It will be noted that in place of the ordinary pair of receiver coils 
employed, there are four coils on the receiver. The coils A and B are in 
series, as are also the coils C and E y and the two groups are in parallel. 
The coils B and E are actuating coils, while the coils A and C are design¬ 
ed to prevent the demagnetization of the receiver or the buckling of the 
receiver diaphragm. Coils B and E are wound in the ordinary manner 
and act upon the receiver diaphragm in the same manner as in the ordi¬ 
nary receivers. The coils A and C are wound in opposition to the coils B 
and E respectively, and their action is to oppose magnetism set up by the 
direct current in the coils B and E. 



Fig. 445. 


The magetism produced by the transmitter battery flowing through 
the coil B is neutralized by that produced by this same current l” c ° 1 ' 
The same is true of coils C and E, and it is evident that as the co l A and 
8 and C and E respectively are in series, the effect of this transmitter cur¬ 
rent will be neutralized, no matter what the length of the line; may be. 
The two groups are placed in parallel merely to reduce the ohimc reS1 ^ 
ance of the entire receiver, so that the transmitter will get its full current. 

It is evident that if the coils A and C were made in the same manner 
as coils B and E, they would oppose not only the magnetism Produced in 
coils B and E by direct current, but also that prodnced by the talking 
rents, and would thus reduce greatly the efficiency of the receiver To ob¬ 
viate this, the coils A and C have a copper sheath over the core and copper 


American Telephone Journal. 



































































356 


TELEPHONOLOGY 


heads on the spool. In actual practice the head and sheath are in one 
piece of copper. The effect of a copper sheath around a core is well 
known. It kills the action of the coil, due to any alternating - currents of 
high frequency. It also reduces the impedance of these coils to alternat¬ 
ing currrent. 

It is evident then that with a receiver of this design we have a bal¬ 
anced receiver as far as direct current is concerned, and that in respect to 
the voice currents we have a receiver in which the action of the primary 
coils B and E is the same as an ordinary receiver, and the action of coils 
A and C is absolutely killed, not only as regards magnetic action, but also 
in regard to impedance. We have then in this circuit actuating coils B and 
E in series with non-inductive resistance A and C, and these resistances A 
and C are in parallel. As this resistance is low and is non-inductive, there 
is no effect from this resistance on the talking current.” 



Fig. 446. Dean Electric Co. Wall Set. 


Such a circuit depends for its action upon the variation of the total 
loop resistance by the transmitter, and the maximum variation should be 
obtained by this method, owing to the low impedance of the receiver, and 
the absence of the induction coil. 

The receiving should be very good as the receiver is in the direct line 
circuit, without any loss due to condensers or coils. 











COMMON BATTERY EQUIPMENT 357 

The circuits so far described represent those in general use, and any 
of them can be used with any common battery board. It is advisable how¬ 
ever to use an instrument circuit especially adapted to the switchboard 
it is used with, and usually supplied by the same manufacturer. 

Fig. 446 shows a standard wall set. The front of the telephone in¬ 
cluding the shelf is made in one piece, thereby exposing the various parts 
of the apparatus. The receiver cord enters the cabinet through a hole so 
located as to prevent the entangling of the cord in the hook when the re¬ 
ceiver is hung up. 



Fig. 447. 


It will be noted that the line binding posts are located inside of the 
cabinet so that the line connections can be brought in from behind the 
back board, thereby concealing all of the wiring when the instrument is 
installed for use. This is rarvdly coming into favor as it not only removes 
unsightly wires from in front of the instrument, but also places them so 
that they are protected from the attacks of the curious. 

In Fig. 447 is shown a metal box instrument particularly well adapt¬ 
ed f or hotel or private house installations. The retaining case is made 
from heavy sheet steel drawn into shape without seams and finished with 
enamel. 

The internal wiring is done with a special insulated wire formed into 
a cable. The outer insulation of this wire has distinguishing colors. Fig. 
448 shows a view of this instrument open with the parts exposed. 


358 


TELEPHONOLOGY 


It is almost a standard practice to use a standard 1,000 ohm Bell and 
2 M. F. condenser for the ringing equipment of common battery instru¬ 
ments. The majority of common battery sets irrespective of their talk¬ 
ing circuits are so equipped, excepting party line instruments. 

Telephones of the desk set type are used to a great extent in common 
battery work. The circuits of a standard set may be seen by referring to 
Fig. 449. In this set it becomes necessary to use a separate containing 
case for the bells and condenser. When the coii is located in base of stand, 
the circuit shown in Fig. 450 is used. 



Fig. 448. 


All modern common battery telephones can be furnished to work in 
connection with the various selective ringing systems now on the market. 
Another'^ excellent feature obtainable with common batterry instruments 
is the ability to equip each phone with a lock-out relay, by means of 
which it is possible to give private service on a line of several telephones. 
Heretofore lock-out instruments have been regarded with suspicion by 
the telephone public, as the words “lock-out” usually- suggest a complica 
tion of springs and wheels with their attendant central office equipment 
which requires additional work on the part of the operator, or which Costs 
a great deal to maintain. -*■’* ' 

The advantages of using a lock-out system are many. Among the 
first to be considered is the fact that this is a ready means of increasing 
the revenue of an exchange without any outlay for expensive line con- 











COMMON BATTERY EQUIPMENT 


359 


struction, as for instance, four telephones equipped with selective ring¬ 
ing and lock-out devices can be placed on the same line, and each one of 
these telephones can be rung without ringing the other parties. When 
any receiver is removed from the hook, the other three parties are 
cut off the line, and the party talking has control of same until finished. 
In this way it is possible to increase the number of telephones and conse¬ 
quently the revenue, without increasing the number of lines, and without 
materially increasing the cost of equipment or maintenance charges. 

One device on the market for accomplishing this result consists of a 
relay of peculiar construction which is attached to each telephone on the 
line, the contacts of the relay keeping the associated transmitter and re¬ 
ceiver circuits normally open. These talking parts are accordingly inope¬ 
rative until the relay is pulled up by current from the central office. 

It can readily be seen that if some means were provided to make it 
impossible for one relay to operate while another on that line was pulled 
up, the fact of one station being in on the line would lockout the balance. 
To provide for this advantage is taken of an effect which is present in 
every central energy line, that of the voltage between the lines being 
greater when the lines are open than when a low resistance, such as the 
transmitter at soffie station is put across. The relay has two windings, one 




of about 1,000 ohms and another of about 20 ohms. When a man lifts his 
receiver from the hook switch, battery flows through the 1,000 ohm winding 
across the line. If no other station is across, there is voltage enough to 
puli the relay up. As soon as this is done the relay contacts close the 
receiver and transmitter circuit and also the 20 ohm winding, thus putting 
a low resistance path across the pair. Since most of the resistance of the 
line is then in the impedance at the central office, the voltage across the 
pair falls too low to pull up any other relay on the line, consequently, t u 
relay at any other station would not get enough current to operate, since 
when the relay is normal the transmitter and receiver ciicults are open 
and a subscriber attempting to get in on the line is locked out. 

































































360 


TELEPHONOLOGY 


The circuit of the relay as applied to a telephone is shown in Fig. 451. 
Inspection will show that a circuit through the high coil is closed by the 
switch hook. The transmitter and receiver are inoperative, their circuits 
being open at the relay contacts. If there is no one else on the line the re¬ 
lay pulls up on operating the switch hook, thus closing the receiver con¬ 
tact and giving battery to the transmitter through the holding coil of 20 
ohms. This holding coil has two functions: First, to hold the armature 
securely after it has once been pulled up, since the low patch o ' the 20 
ohm coil and transmitter will drain practically all the current from the 
1,000 ohm winding. Second, to act as a retardation coil for the voice cur¬ 
rents. The condenser and receiver are in a shunt circuit around this 20 
ohm coil, consequently, the self induction of this coil will force the voice 
currents to go through this condenser path, thus the telephone equipped 
with the lock-out does not require any induction coil. 



From the foregoing description it will be seen that the action of this 
lock-out is automatic. No additional operation is required by either the 
operator or the subscriber. The action of closing the hook switch throws 
the relay into circuit and as soon as it pulls up, throwing the low path 
across the line, no other relay will operate because all the available cur¬ 
rent is drained from the line. 

In practice the relay is made as shown in Fig. 452 and is mounted on 
the telephone as in Fig. 453. 

The adjustments of the relay are few, since from the foregoing de¬ 
scription it will be seen that proper adjustment consists in getting the re¬ 
lay to pull up at one voltage and not to pull up at a lower voltage. The re¬ 
lay is provided with an adjustable banking arm which controls the dis¬ 
tance of the armature from the pole pieces. By bending this brass bank¬ 
ing arm the distance of the armature from the pole pieces and the voltage 
at which the relay will pull up may be easily and effectively controlled. 

























COMMON BATTERY EQUIPMENT 361 

The adjustments, if any be needed, are made as follows: First, after 
connecting telephone to line, lift the receiver and see that relay pulls up, 
if not, it may be made to do so by adjusting the brass banking arm attach¬ 
ed to the armature, so that the relay armature is brought nearer the pole 
pieces. Second, have another party get in on the line, and work hook 
switch at station being adjusted. The relay should not pull up when the 
second station is across the line. If the relay does pull up under this con¬ 
dition, it may be adjusted by bending the brass banking arm to throw the 
armature farther from the pole pieces. 



Fig. 452. Fig. 453. 

It is only in rare cases that any adjustment is necessary. Under nor¬ 
mal conditions of p^rty line work where all the stations are close together, 
the relays will work as they are sent adjusted from the factory. 

Where there is a larger line resistance between the first and last sta¬ 
tion on the line, the line voltage at the near station may not be lowered 
enough when the far station is across the line to prevent the near station 
from getting in. In this case, the relay at the near station will have io 











362 


TELEPHONOLOGY 




be adjusted by throwing the armature further from the pole pieces, so it 
will not pull up when the far station is across the line. 

The button shown in Fig. 451 is for the purpose of handling a revert¬ 
ing call. Central tells the originating party to hold his button until the 
second party answers. This button is in the low circuit and when that is 
open a second party can get in on the line. 

The relay at the originating station is held up by current through the 
1,000 ohm winding, consequently, this station can hear the second one an¬ 
swer. The originating party then releases the button, thus giving bat¬ 
tery to his own transmitter and the two are in on the line. 



Fig. 454. 

While the general method of calling the central office from the tele¬ 
phones has been referred to no detailed description o. the means employ¬ 
ed has been given. While visual signals may be employed, their use is 
now almost entirely confined to private branch exchange work, a private 
branch exchange being a small switchboard located in a building or other¬ 
wise, with the telephones in the immediate vicinity connected thereto, this 
board being connected with the main exchange by means of trunk wires. 

Small incandescent lamps are universally used in the larger boards 
and a relay becomes necessary to operate the lamp as it cannot be placed 
in series with the line, and as it is desired to economize in space as much 
as possible. The relays are therefore mounted in a frame separate from 
the switchboard, usually in another room, and are connected to the lamps 
as shown in Fig. 454. 

The following description by J. C. Kelsey, of the standard circuit in 
general use by the Bell Companies, is taken from the American Telephone 
Journal. It describes in detail this circuit, which is in extended use. The 
circuits of the telephones are not shown in all the figures as these can be 
any of the forms previously described. 

“Lamp signals are used as shown in Fig. 455, and by making them 
depend upon the relays, R 1 R- and R s , the closing of the contacts of which 
completes circuit through the battery and a lamp of proper pressure for 
the battery, which may be assumed to be twenty volts, (11 storage cells) 
the act of taking the telephone off the hook will light the respective lamp, 
as station No. 1 lights lamp L 1 . To insure that the operator shall observe 
the signal an additional circuit is shown in Fig. 455, which should be par¬ 
ticularly observed, as it is the basis of the common night bell signal. 
Through NBR, the night bell relay, all current passes to the lamps. If any 
lamp is lighted, it takes enough current to magnetize this relay, so 































COMMON BATTERY EQUIPMENT 


363 


when any lamp lights, the night bell relay is pulled up, and sounds a 
vibrating bell from a separate battery, which calls the operator’s atten¬ 
tion.” 

“Fig. 456 shows one line, with the relay, R', and night bell relay, 
NBR. The party taking the telephone off the hook, energizes R 1 , causes 
NBR to close its contacts through VB, the vibrating bell. But means 
must be provided for the operator to talk to the parties calling. There¬ 
fore the jack, J, is connected to the line, tip T, to the positive side, ring R 
to the negative side, and the sleeve S, open, between the relay, and the 
telephone.” 



FIG. 6* 


Fig. 455. 



“We may also assume that the positive terminal of the battery is 
earthed, so that in our drawings, any connection shown as earthed, as L 1 , 
really means that it is connected to the positive terminal. Convenience in 
drawing also demands that several batteries be shown, but all of which 
are the same battery, if the grounded connection is shown.” 

“If instead of three stations, we consider from now on, one of not less 
than one thousand, the multiple board will be composed oi live sections, 
and each operator will have the entire thousand lines, terminating in 
jacks, within her reach, which may be represented as in Fig. 457 where 
j> J 2 J 3 ^ an( j jr. are the multiple jacks, and J“ the answering jack, 
directly underneath the lamp L'. The sleeves are connected in multiple 
for reasons soon to be explained.” 



“In the local battery service, on multiple boards, to keep the- drop 
from falling, when a multiple operator rings on the line, the jacks are 















































































































364 


TELEPHONOLOGY 


made, so that the entrance of the plug cuts off the signal apparatus, and 
leaves the operator in direct connection with the subscriber. If in com¬ 
mon battery service, when the multiple operator called a party, and he an¬ 
swered, the lamp would light up in front of the answering operator, and 
she would plug in, only to find that some one else was using the line, mak¬ 
ing much confusion. It becomes imperative that the entrance of the plug 
shall cut off the line battery and relay, and reintroduce battery to the sub¬ 
scriber through the cord circuit. This must be done electrically by the 
presence of battery on the sleeve which shall flow through a cut-off relay, 
from the sleeve of the jack. This act opens the line between the relay and 
the first jack, as shown in Fig. 458, COR being the cut-off relay, actuated 
by the entrance of any plug.” 

“As battery exists on the sleeve of the plug, assume a lamp in series, 
between the battery and the sleeve, which lights when the plug is inserted 
in the jack, according to Fig. 459, at the same time the cut-off relay is 
opened. But opening the cut-off relay deprives the subscriber of battery, 
and he cannot talk, so the act of plugging must reintroduce battery, and 
this is the origin of the vicious clicking in the ear just before central 
speaks. It is caused by the cutting off process, for the induction coil of 
the telephone is charged. The sudden opening of the line allows it to dis¬ 
charge and expend itself in the receiver.” 



“If all the cord circuits were furnished with battery as shown in Fig. 
460, the system would be in a sorry plight from cross-talk, so impedances 
are inserted between the battery and the sides of the cord circuit, accord¬ 
ing to Fig. 460a, which shows an ordinary repeating coil, with the middle 
terminals attached to the battery. Each winding of the coil is about 20 
ohms, with enough iron in the core to prevent any stray impulses from 
other cord circuits.” 

“Still the circuit is deficient, for at present nothing affects the cord 
lamp, whether the subscriber’s telephone is off the hook or not. How shall 
this lamp be made to signal the position of the receiver? The answer is, 
put in another relay, placed in the cord circuit according to Fig. 461, be¬ 
tween the ring of the plug and the battery in such a manner that it shall 
control the lamp circuit.” 

“But we all know that it is undesirable to have a relay directly in the 
talking circuit. How can we obviate this objection? By providing a path 
for the voice currents around the relay that is now inductive. 

“Fig. 462 shows the windings of the non-inductive relay. In this 
case, the copper winding or the inductive winding is wound close to the 
core, and the german silver winding of few turns on the outside. The non- 
inductive winding has nine times the resistance of the inductive winding, 
and consequently takes but a small fraction of the exciting current, and 
only weakens the felay but slightly. 
















COMMON BATTERY EQUIPMENT 365 

“If a lamp is paralleled by a shunt of one-third its own hot resis¬ 
tance, it is unable to receive sufficient current to heat the filament to more 
than a dull red. This is taken advantage of in extinguishing the cord 
lamp. Fig. 463 shows the non-inductive relay contacts in the act of clos¬ 
ing a resistance 1/3 R, about the lamp R, which will cause the filament to 
burn a dull red. In addition, an opalescent shade is placed over the lamp, 
which, when the filament is reduced to a dull red, gives the effect of total 
extinguishment, and which, when lighted, mellows the light rays so that 
they are not offensive to the eye. 



Fig. 460. Fig. 460a. 


“Fig. 464 shows the application of the shunt, 1/3 R, to the answering 
cord circuit. The act of plugging in cuts off battery, restores it again, 
and if the receiver is off the hook the relay R 2 is energized, and closes its 
contacts, putting 1/3 R in shunt with cord lamp, CL, and putting CL out. 
When the subscriber hangs up the receiver, battery can no longer flow 
through R 2 because the circuit is open. It therefore releases its contacts, 
which open circuit of 1/3 R, and allows lamp, CL, to burn at its full 
brightnesss. The operator knows that the subscriber has hung up the re¬ 
ceiver, and pulls down the connection. 



“So far we have considered only the answering part of the cord. The 
calling cord possesses the same characteristics of the answering cord as 
regards the position of the relay, and the action of the calling lamp. The 
general characteristics of the complete cord are shown in Fig. 465. The 













































366 


TELEPHONOLOGY 


calling cord is provided with keys, both for ringing, talking and listening 
to the subscriber. Fig. 465 shows the four sections of the repeating coil, 
R 1 P 1 and R 2 P 2 belonging to the answering cord, and R 3 P 3 and R 4 P 4 the 
sections belonging to the calling cord. They are all wound on the same 
core, and serve the same purpose as they did in local battery service, that 
of connecting grounded and metallic lines without unbalance. When both 
parties have their receivers off the hooks, both lamps, ACL and CCL, are 
out, because relays R 2 and R 3 are energized by the current passing out to 
the subscribers’ stations through them. When both parties hang up, R 2 
and R 3 release contacts, because no current flows. 


.. ij 

/7V'i 

t7T 

v' 0 

1 

' ' V 

< 1 

LJ 1 il 

I : 

" 1 

• i | 

■ i 
« i 

■ 1 





Fig. 462. 






Pl <3 

R 


in 

Ar»u Ht 

_ J 


Fig. 463. 


“‘The repeating coil shown in Fig. 465 consists of four sections of 
wire, each one having two terminals brought out. All four coils are 
wound on the same core. When used with common battery, the coil 
should be connected up as shown in Fig. 465. If used with local battery 
the outer terminals of R 1 P 1 and R 2 P 2 are connected to one-half of the 
line and the inner terminals connected together. Similarly the outer ter¬ 
minals of R 3 P 3 and R 4 P 4 are connected to the other half of the line, and 
the inner terminals connected together. 



“In this manner battery is supplied to all cord circuits of this kind, 
and the impedance of each of the windings guards against the invasion of 
cross-talk, while the repeating coil, as a whole, removes the possibility of 
unbalance. Each half of the coil repeats into the other half, just as if the 
battery was not present. It seems strange that a wave can pass through 
the battery solution and not interfere with the induced wave it has creat¬ 
ed, but the battery has such an infinitely small resistance that it aacts like 
a short circuit path, where everything can pass. 

“The development, so far, shows one cord circuit ending in two plugs, 
the answering and the calling exactly alike. But the calling end is equip¬ 
ped with a double key, which permits of ringing with one pair of contacts 
and listening with the other. According to Fig. 466 the ringing key is so 
arranged as to cut off the circuit behind, so that ringing back in the wait- 

















































































COMMON BATTERY EQUIPMENT 367 

ing subscriber’s ear is avoided. Another reason is that the half of the re¬ 
peating coil and battery would short circuit the generator current for 
single line ringing, and the ground at the battery would prevent party 
line ringing. The listening set is connected in bridge, so that the opera¬ 
tor may talk to either answering or calling parties. 



Fig. 466. 


“Fig. 466 shows a local battery operating set, which can be bridged 
on any pair of cords in the operator’s position. The system is usually so 
large that there are many branch exchanges, that necessitate as many or¬ 
der wire connections, usually accomplished by a row of buttons, generally 
in strips of ten, at the right hand side of the switchboard. Depressing 
any one of the keys, puts the telephone set in direct connection with the 
“B” operator, at the receiving end of the order wire, belonging to that 
key. 

“This is shown in Fig. 467 in which O 1 K', O 2 K 2 , etc., are the order 
keys, placed in the operating set in connection with “B/’, “B. ”, etc. 



“At night, the various “B” operators are not at their positions, from 
lack of business, and it is customary fbr an “A” operator, who wants a 
trunk call, to depress the order key of the exchange desired, and ring on 
the order wire. This operates a bridge drop at “B” end of the order wire, 
and lights a lamp, whcih will cause the night bell to ring. This calls the 
night operator to the receiver, who takes the order. The key used for 
trunk ringing is shown in Fig. 468, as RDK, for the ring down key is so 
arranged that any of the “A’’ operators may ring on any of the order wire 
keys without ringing back. 

































































368 


TELEPHONOLOGY 


“Looking at Fig. 466 it is seen that if the calling cord is plugged up, it 
lights the calling lamp, and the operator, throwing her listening set across 
the cord circuit, will put out the lamp as if the called party had answered, 
because the receiver and the secondary of the induction coil act like a sub¬ 
scriber’s instrument. This would cause a confusion of signals, which is 
remedied by the addition of a condenser, placed at K in Fig. 468. The con¬ 
denser also saves the operator’s ear from a click every time she throws in 
her listening key, because it prevents the sudden pull of a 24 volt battery 
on the receiver diaphragm, and does not in the least interfere with trans¬ 
mission. 



Fig. 469 is a local battery operator’s set, with T as the transmitter, 
B, the four-volt local battery, P, S and R, the primary, secondary, and re¬ 
ceiver respectively. Suppose that it is desired to have all the transmit¬ 
ters on the common battery, ranging from twenty to forty volts. Then 
according to Fig. 470, the transmitter is placed in the primary circuit. 

“But if one puts the receiver to his ear he will find something wrong, 
for there is a frying noise, and the transmitter will become very hot. This 
is due to the ability of the more powerful storage battery to force exces¬ 
sive current through the transmitter, and additional resistance must be 
added, sufficient to prevent the transmitter from heating or frying. 



Fig. 469. 



“When several talking circuits are connected to the same bus bars, 
there is a likelihood of cross talk. If every talking circuit was connected 
directly to a large storage battery, the cross-talk might be avoided, 
though there is still a probability of its presence; It is not practical to 
connect directly to the battery, for there must be suitable switchboards 
with apparatus provided for proper distribution. Therefore, to prevent 
cross-talk in the primary circuit, the resistance must be changed to induc¬ 
tive resistance, called retardation. This retardation guards against the 






















































COMMON BATTERY EQUIPMENT 369 

entrance of stray electrical impulses, because all electrical impulses have 
fT av ^ rsion passing through coils with iron cores. It is in this manner 
that the repeating coil windings, around an iron core, guard the cord cir¬ 
cuit against the intrusion of impulses. This is shown in Figr 471 in 
which RET is the retardation coil. 

But a serious objection arises. We have deliberately inserted a coil 
with an iron core directly in the transmitter circuit. This will cut down 
voice currents, so that the transmitter is virtually useless. One can hard¬ 
ly hear hard tapping of the transmitter. Something must be done to over- 
come the retardation effect of this coil, so that the impulses generated by 
the transmitter will not be destroyed. This is accomplished by the ever 
useful condenser. It is connected in the primary circuit, so as to divide 
it equally, the transmitter and primary in one half, and the retardation 
and battery in the other half, as hown in Fig. 472. 




Fig. 472. 


“The answering cord is connected to the repeating coil on the tip, or 
positive side, and to the repeating coil on the ring or negative side through 
the relay AR. Looking at Fig. 473 we find the sleeve of the plug connect¬ 
ed to the negative battery through a lamp, AL. As there is twenty-four 
volts battery in this particular system, it seems fitting to wind the cut-off 
relay, of equal resistance to the lamp, so that it will divide the voltage of 
the battery. Supposing one-tenth of an ampere is necessary to heat the 
filament of a 12-volt lamp, then the hot lamp resistance is about 120 ohms. 



This would make the resistance of the cut-off relay also 120 ohms, which 
we will assume to be correct. If the lamp has a hot resistance of 120 
ohms, then one-third R will be 40 ohms. When the operator inserts the 
answering plug into the jack of a calling line, the lamp, AL, does not 
light, because AR has become magnetized, owing to the fact that it is in 
the line of battery supply to the subscriber. AR being energized, pulls up 

24 





























































































370 


TELEPHONOLOGY 


its contacts, bringing the shunt resistance 1-3 R, around AL, and robbing 
it of nearly all its current, which provides a supervising signal. 

“It is in the calling cord that most of the apparatus is used. It can 
not be said that the primary circuit of the transmitter belongs to the call¬ 
ing equipment, yet the secondary part of it does, for the operator has the 
power of putting her talking set on every pair of cords. Looking at Fig. 
473 we find that the only similarity to the answering side is the sleeve 
connection. The sleeve is connected to battery through a 12-volt lamp, 
CL, which is lighted upon plugging into a jack of a line wanted, the cut¬ 
off relay sharing the average twenty-four volts with the lamp, CL. As in 
the answering cord, when the receiver is off the hook, relay CR is ener¬ 
gized, being in the path of current to the called subscriber. This causes 
the relay contacts to close, bringing 1-3 R around the lamp, CL, and ex¬ 
tinguishing it, providing a supervisory signal. 



“The tip of the calling plug does not connect directly to the positive 
terminal of the repeating coil. It passes through the contacts of the ring¬ 
ing key RK. Also the ring of the plug has to pass through the contacts 
of key, KR, thence back to the repeating coil terminal through the relay, 
CR. Were it not for such a connection, when the operator rings a party, 
she would ring back in the waiting party’s ear. So when she rings, the 
hard rubber cylinder shaped piece, directly under the cam handle, wedges 
the two springs, T 1 and R-, and raises them simultaneously against the 
generator contacts, which allows the ringing current to flow through the 
subscriber’s bell. When she releases the cam handle of the ringing key, 
the wedge forces the key to normal. 

“The operation of the talking key, LK, is different. It does not open 
any circuit. It only bridges the listening set across the line, so that the 
operator may talk to either party. The reverse action of the cam handle 
forces the wedge underneath against springs, T and T, raising them into 
contact with the secondary terminals.. But in this case, the wedge has 
proceeded so far as to prevent its recovery, except manually. This is neces¬ 
sary, because the operator may have to write as well as talk. 

“The strip of order keys, O' K 1 , O 2 K 2 , etc., are connected by a 
strap directly to the ring down key, RDK. The condenser is placed be- 






































































































COMMON BATTERY EQUIPMENT 371 

tween springs R of ring down key, and contact is made when the listen¬ 
ing key is used. 

“Fig. 474 shows a complete connection between two common battery 
subscribers. Both telephones are off the hook, both cord relays are ener¬ 
gized and therefore both lamps are out. Both cut-off relays are open, and 
consequently, the line lamps are both out. If one party hangs up the re¬ 
ceiver his supervisory lamp lights. The party whose lamp is still out is 
not ready to clear out. If another party is desired, the subscriber is sup¬ 
posed to raise and lower the receiver hook, which flashes the lamp and at¬ 
tracts the operator’s attention. 







i 



i? 





i? 


fiPjCTi 




■H'littl'M; 
2 


c-: 




-ft 











■_> 



JL 




>« 

< 0 


A 


Fig. 475. 

“Fig. 475 shows a complete connection between two parties, and an¬ 
other operator is in the act of testing. The original sleeves of the jacks 
of the now busy line had a potential of that of the earth. If the operator 
had tested before the preceding operator had taken possession of the line, 
the touch of the tip of the calling plug to the sleeve of the jack would have 
had no result. 

“If the second operator touches the tip of her plug to the sleeve of 
jack which is busy, the battery, the battery existing on the sleeves will 
find a path through the tip of the plug, and back to ground through one 
quarter of the repeating coil. 


“Touching the tip to the sleeve, the battery of the upper cord circuit 
flows through the lamp to sleeve, thence through the contact of the key, 
to the quarter of the repeating coil, R ! P , through to the positive side of 
the battery. 














































































































































































372 


TELEPHONOLOGY 


“The operator’s key being closed, the wave induced by this energy 
passes through the only path it can find, the bridged telephone set. If the 
subscriber is waiting at the answering cord end he will hear the test, be¬ 
cause his half of the coil also induces a rush of current which finds a path 
through his telephone set. 

“Fig. 476 shows the outline of a busy test, just as the tip is withdrawn 
from the sleeve. The plug is shown without the ring and sleeve, as these 
are not used in receiving a test. It shows the listening key closed, putting 
the receiver across the line. 


41 


iiii in 


«c: 





Fig. 476. 


“Fig. 477 shows the outline of a talking circuit between two parties o e 
a common battery repeating coil system, with the old local battery tele¬ 
phones still in use. AR and CR are the cord relays, and the RP’s the quar¬ 
ters of the repeating coil. While the batteries are shown in the tele¬ 
phones their presence is in no sense necessary to the operation of the sys¬ 
tem, and they are in fact never used.” 



The foregoing description o f a common battery system if carefully 
studied, will lead to a good understanding of the various parts, their pur¬ 
pose and operation. The circuit as described is in extensive use, but is 
not the circuit now employed by the Bell Companies. This late circuit is 
somewhat different in arrangement and a description of same will be 
found elsewhere. 

Typical of moden practice is the switchboard installed at St. Louis, 
Mo., by Stromberg-Carlson Telephone Mfg. Co. This is probably the 
largest single switchboard in the world. 





































































COMMON BATTERY EQUIPMENT 373 

_ T h( r line a . nd C0 F d pircuits are shown in Fig. 478. The line circuit is 
of the three wire bridging multiple type, employing a cut-off relay for re¬ 
moving the line relay from the circuit during a conversation. 

-A.s shown in Figure 478, the outside line cables terminate on one side 
of the Mam Distributing Frame, and jumper across to the protective ap¬ 
paratus located on the oppositive side of the frame. From the arrester 
equipment the circuit is continued to the side of the Intermediate Distrib¬ 
uting Frame nearer the Main Frame. This side of the Intermediate is 
termed the multiple side, the cables leading to the multiple jacks being 
soldered on the same clips with those from the Main Frame. On the sec¬ 
ond side of the Intermediate Frame two sets of cables also terminate, one 
running to the answering jacks in the regular subscribers’ positions of the 
switchboard and the other to the relay rack. The two sides of the Inter¬ 
mediate Distributing Frame are connected by means of triplex jumper 
wires. 



Fig. 478. 

S. C. Co. Line and Cord Circuit. 


Now in considering the action of the circuit it will be borne in mind 
that at the subscribers’ instrument a condenser, in series with a ringer, is 
connected across the line. Under normal conditions the path of the bat¬ 
tery current through the instrument is interrupted by the presence of the 
condenser, but up raising the receiver from the hook, a complete circuit is 
established through the transmitter and induction coil. Tracing the cir¬ 
cuit back to the central office it may be followed through the two distrib¬ 
uting frames, through the “break” contacts of the cut-off relay, thence 
through the two windings of the line relay and to battery. Being ener¬ 
gized by this current, the line relay closes its one make contact, complet¬ 
ing a local circuit from the positive side of the battery, through the line 
lamp, the low resistance line pilot relay, and to the negative side of the 
battery. The illumination of any line lamp thus causes the line pilot re¬ 
lay in the same position to close a set of make contacts, throwing the line 
pilot lamp, which is located behind a large white opal beneath the answer¬ 
ing jacks, directly across the battery. A second make contact is provided 
on the line pilot relay, that auxiliary pilot lamps may be lighted on the 
monitor’s desk as an aid in supervising the work of the operators, and in 
some cases for lighting minor line pilot lamps on adjacent positions, that 
each operator may more readily notice unanswered calls on the positions 
to her right or left and lend assistance to her neighboring operators. The 
circuit o each major line pilot lamp throughout the board is completed to 
the negative side of the battery through the winding of a low resistance 




























































































374 


TELEPHONOLOGY 


relay located in the first position. In case the switch in this position is 
closed, the make contact of the latter relay completes a battery circuit 
through a vibrating bell as a night signal. 

The operator, when she sees a line lamp flash, raises one of the an¬ 
swering cords—the cords nearer the face of the board—and inserts the 
plug in the jack immediately below the glowing signal. At once a circuit 
is established from sleeve battery through the lower coil of the relay 
marked answering supervisory, out on the sleeve side of the plug to the 
thimble of the answering jack, and thence through the winding of the cut 
off relay and back to battery. Energized by this current the contacts of 
the cut off relay are opened, thereby removing the line relay from the cir¬ 
cuit. As the line relay’s circuit is no longer complete, its armature drops 
back and the line lamp is extinguished. From the sleeve side of the an¬ 
swering plug a second circuit may be traced through the sleeve spring of 
the answering jack, out on the line and back to tip spring of the jack to 
tip side of plug and through the upper coil of the previously mentioned 
supervisory relay. The relays used in this cord circuit are o: a peculiar 
construction as shown in Fig. 479. 



Fig. 479. 

Each relay in effect consists of two separate relays, with a mechani¬ 
cal interaction between their respective armatures. The armatures are 
located between the relay spools, and so constructed that both are normal¬ 
ly held at the upper end of their play by a spiral spring. Stirrups from 
the ends of the armatures hold the relay contacts in the open position. 
Now when the lower coil is energized the lower armature is attracted 
downward against the action of the spring, allowing the upper armature 
to drop with it, and closing the relay contacts. But, when the upper coil 
receives current, its armature is attracted upward, again opening the up¬ 
per set of contacts. When closed, the upper contacts on either relay com¬ 
plete circuits from battery to their respective answering and calling su¬ 
pervisory lamps located on the keyboard directly in front of the corres¬ 
ponding cord pair. Normally, as is the usual practice, both lamps are 
dark, and a ter plugging into the answering jack no change occurs ?s cur¬ 
rent is flowing through both coils of the answering supervisory relay. 

Besides serving the function of supervisory relays the two windings 
on these relays also act as impedance coils, blocking completely the path 










COMMON BATTERY EQUIPMENT 


375 


of the alternating voice currents in the direction of the battery, and at 
the same time maintaining the battery feed for talking purposes at a con¬ 
stant value. 

Having plugged in, the operator throws the corresponding cord key 
into the locking or listening position, which bridges the operator’s set 
across the cord and enables her to speak to the calling subscriber. After 
ascertaining the number desired, she raises the calling plug of the same 
cord pair and touches the tip of the plug as a busy test, to the thimble of 
the nearest multiple jack on the required line. 

Referring to the line circuit, it will be seen that the thimbles of jacks 
on unengaged lines are at the potential of positive battery, and as the tip 
of the calling plug at this time is at the same potential, no sound will be 
heard and the operator proceeds to plug into the jack. But in case the 
tested line is in use, current flowing from the sleeve of the plug, over 
which this second connection has been established, to the cut-off relay of 
the tested line, materially reduces the potential of every thimble multi- 
pled with the engaged jack. At the touch of a plug to such a jack there 
is a rush of current from the engaged thimble through the tip side of the 
testing cord, through the make contact of the listening key, and through 
a special winding on the operator’s induction coil, completing the circuit 
to positive battery. A distinct click is thus produced in the operator’s re¬ 
ceiver, and she at once informs the calling subscriber that the line is 
“busy.” Owing to a break contact in the listening key the busy click is 
not heard at the subscriber’s instrument. 

In plugging into the called subscriber’s jack, battery at once flows 
through the lower coil of the calling supervisory relay and over the sleeve 
of the calling plug to the cut-off relay, as in the case of the calling line, 
and the “busy” also put on the multiple. 

A non-inductive resistance wound on the line relay is included in one 
side of the line circuit, which without sacrificing the efficiencv of the re¬ 
lay, serves as a protection from short circuits on lines using pulsating 
grounded party ringing. In this case it becomes necessary to reverse the 
polarity of the battery on the line relay. 

Returning to the cord circuit, it will be seen that a circuit is complet¬ 
ed at this stage of the connection through the upper contacts of the calling 
supervisory relay and calling supervisory lamp, as only the lower relay coil 
is energized. To throw ringing current on the line, the key is pulled in 
the non-locking position, the generator circuit being connected to the two 
outer springs of the ringing key. The two break contacts shown on this 
key cut the answering portion of the cord circuit off, that current may not 
pass back over the line and produce a buzz in the calling subscriber’s in¬ 
strument. At first glance it might appear that this act would interrupt 
the flow of the battery current, which holds up the cut-off relay, but while 
the circuit established through the lower coil of the supervisory relay is 
broken, a new circuit is established to negative battery over the “make” 
contact on the sleeve side of the ringing key, and through the generator 
circuit as will be described later. Upon the called subscriber’s receive*' 
being removed from the hook, a current is established over this line as on 
the calling line, and the upoer coil of the calling relay being energized, the 
calling lamp circuit is broken. 

The parties are now in a position to converse, and the action of the 
talking circuit will next be considered. Let us assume an instant at which 
the transmitter diaphragm at the calling station is at the extreme out- 







376 


TELE PHONOLOGY 


ward end of a vibration caused by the voice of the party talking. The 
transmitter resistance is at this moment at its maximum, and the current 
flow at the minimum. Obviously, as the current flow is kent constant by 
the impedance of the supervisory relay windings, the potential at the two 
condensers in the cord circuit is at a maximum, and the condensers re¬ 
ceive a charge. At the next instant the transmitter diaphragm has swung 
to the opposite extreme, and due to the lowered resistance, the potential 
at the condensers drops and they impress their charge on the circuit. In 
this manner the transmitters receive a varying amount Oi current, while 
not the least fluctuation is noted in the total battery flow. Owing to the 
induction coils in the local instruments, the talking currents are alternat¬ 
ing in character, and pass through the condensers from one line to an¬ 
other without opposition, though in effect the action would be much the 
same without induction coils at the local stations, the continual charge 
and discharge of the condensers being equal, though in reverse directions 
on opposite sides of the cord circuit. These condensers also ser^e the im¬ 
portant function of separating the cord into two sections for purposes of 
supervision. 

If, after a connection has been completed, the operator wishes to “lis¬ 
ten in” the talking circuit between the subscribers would be broken but 
for a shunt path, which was established around the listening key through 
the lower contacts of the calling supervisory relay, when the lower coil of 
the latter was energized. Upon both parties hanging up, the circuit 
through the upper coils of the supervisory relays are broken and both su¬ 
pervisory lamps at once appear as a disconnect signal. As the party orig¬ 
inating a call is supposed to control a connection, the answering supervi¬ 
sory lamps are connected to negative battery through the low resistance 
winding of a supervisory pilot relay. The latter causes a lamp to light be¬ 
hind a red opal, near the line pilot lamp at any time an answering super¬ 
visory lamp may flash. 




The operator’s circuit used in connection with this line and cord cir¬ 
cuit is shown in Fig. 480, the two leads marked tip and sleeve running re¬ 
spectively to the outer springs on the tip and sleeve sides of the listening 
keys. 

In this manner the receiver, in series with the secondary of the induc¬ 
tion coil, is bridged across a cord circuit whenever a listening key is 
thrown. A condenser also is inserted in this portion of the operator’s cir¬ 
cuit, that battery from the cords may not find a path through the opera- 



























































COMMON BATTERY EQUIPMENT 377 

tor’s set. The induction coil used in this circuit is provided with four sep¬ 
arate windings, the primary, secondary, test and tertiary. The practice 
of providing separate primary and secondary windings enables the opera¬ 
tor’s transmitter to be isolated from the line, thus securing the maximum 
percentage of variation in the resistance of the transmitter circuit as in 
local battery practice. Otherwise the action of the transmitter circuit is 
quite similar to the talking circuit previously described. The test wind¬ 
ing, to which reference has already been made, is of very high resis¬ 
tance in order that an appreciable amount of current may not be drawn 
from a busy line jack when tested, and serves as a primary winding only 
when the “busy test’’ operation is performed. The terminals of the ter¬ 
tiary winding are in most exchanges wired to listening in jacks or keys 
located on the monitor’s desk, this winding being designed only as an aid 
in observing the work of the various operators. 

Fig. 481 illustrates the latest practice adopted in the Stromberg-Carl- 
son Telephone Mfg. Co.’s four party harmonic ringing systems. The key 
used in this system consists of the usual combined listening and ringing 
cam, and three ringing buttons. By pressing the cam in the ringing direc¬ 
tion, with all the buttons normal, a circuit is established from the outer 
spring on the tip side of the ringing key, through the series of contacts on 
the buttons, and thence through a 200 ohm ringing relay to the 16 cycle 
generator, completing the circuit to the sleeve side of the ringing key 
through battery, and a low non-inductive resistance. 

It may now be seen how the battery current is supplied over the 
sleeve side of the calling plug to hold the cut-off relay energized, during 
intervals while ringing current is impressed upon the line. The non-in¬ 
ductive resistance is inserted in this circuit only as a guard against exces¬ 
sive flow of current due to accidental short circuits which might occur 
upon the line. In order to ring a party with the 33 cycle frequency, the 
button adjacent to the ringing cam is depresed, cutting off the remaining 
keys, and establishing a circuit through a second ringing relay to the 33 
cycle alternator; the ringing cam is then thrown in the usual manner to 
call the party, the button remaining down until either the ringing cam is 
thrown in the listening position or another button is depressed. Parties 
rung by the 50 and 66 cycle frequencies are obtained in a similar manner 
by pressing the second and third buttons, respectively. 

The “make” contacts of the four ringing relays are wired in parallel, 
and by closing any one a circuit is established through the ringing pilot 
relay, placed behind a green opal beside the line and supervisory pilots. 

Thus far connections only have been discussed which might be com¬ 
pleted by one operator, in the multiple jacks, appearing on her own 
switchboard. In systems consisting of more than one central office, pro¬ 
vision must be made for trunking the calls between the various offices and 
a part of the operators in each exchange are designated as the trunking 
or “B” operators, performing no service other than completing incoming 
calls from neighboring offices. Let us assume as an illustration of trunk¬ 
ing practice that a subscriber whose line terminates in an exchange de¬ 
signated as East, wishes to speak with No. 672 on the “West” exchange. 
The regular operator at the “East” office on whose position the line signal 
appears answers the call as usual with one of her answering cords and 
learning that the desired party is on the west office, presses an order wire 
button which connects her head set to a line terminating in the operator's 
set on a “B” position at the “West” office, as shown in Fig. 482. 




378 


TELEPHONOLOGY 


A switching key is included in this circuit at the “B” position in or¬ 
der that the order wire may terminate in a visible signal at times when an 
operator is not continually at the position. With the switching key in the 
position shown, a circuit is established from battery through the relay, 
the “A” operator’s head set, as shown in Fig. 480 and one of the “A” ope¬ 
rator’s order wire buttons, when the latter is depressed, causing the 
lamp to light in the trunk position behind a large white opal similar to 
the line pilot. This pilot lamp is not used, however, at times while an ope¬ 
rator is constantly at the position. 

The “A” operator at East now instructs the “B” operator at “West” 
that “East” wishes No. 672. The “West B” operator now selects an un¬ 
used trunk from the “East Exchange,” say No. 6, which terminates in a 
plug on her position and repeats back to the “A” operator at “East,” “No. 
672 on trunk No. 6.” This trunk terminates at the “East” office in a 
series of jacks multipled throughout the board in much the same manner 
as the regular subscriber’s multiple, and the “A” operator at the latter 
exchange now proceeds to complete the connection by placing her calling 
plug in the nearest trunk jack No. 6. 


‘A’ Amhd fl poi 



Fig. 482. 



Referring to Fig. No. 483, the trunk circuit diagram, it will be seen 
that in place of the cut off relay, which was used on the line circuit, an im¬ 
pedance coil has been substituted through which current from the lower 
coil of the calling supervisory relay of the cord circuit is established from 
the calling plug of this cord circuit over the sleeve side of the trunk to the 
West Exchange, through the break contact of the relay C, and the wind¬ 
ing of the relay A, completing the circuit back to the “East” Exchange on 
the tip side of the trunk. However, the winding of the relay A is of very 
high resistance and sufficient current does not find its way back to the 
“East” Exchange to extinguish the calling supervisory lamp. The arma¬ 
ture of relay A is pulled up by this current, and its one “make” contact 
throws one of the windings of the relay B directly across the battery. This 
latter relay at once causes one contact to break and another to make estab¬ 
lishing a circuit from negative battery through the disconnect ; lamp, the 
“make” contact of relay B, the “break” contact of relay D and returning 
to the positive side o p battery. Meanwhile the “B” operator at West Ex¬ 
change has raised the trunk plug and performed the busy test upon the 
desired line in the usual manner, the circuit being traced from positive 
battery through the test winding of the operator’s induction coil, the up¬ 
per “break” contact of the relay D, the inner contacts of the ringing key 











































































COMMON BATTERY EQUIPMENT 


379 


to the tip of the plug. Assuming that no “busy” click is heard, she pro¬ 
ceeds to plug into the jack No. 672. A condition quite similar to the reg¬ 
ular cord circuit’s action is here encountered, current flowing from nega¬ 
tive battery through the winding of the relay D, out on the sleeve side of 
the plug and energizing the cut-off relay of the line. The upper make and 
break contact of the relay D, removes the test winding of the operator’s 
induction coil from the circuit, and completes the tip side of the trunk cir¬ 
cuit through from this direction to the repeating coil R. The lower 
“break” contact of the relay D opens the circuit that would otherwise 
have been established through the disconnect lamp, while a new circuit is 
completed from positive battery through the “make” contact of the relay 
D and the break contact of the relay E, the ringing lamp and to the nega¬ 
tive side of battery. The “B” operator now rings on No. 672, and con¬ 
tinues to ring at intervals until the called subscriber answers, which is 
indicated to her by the ringing lamp associated with this trunk being ex¬ 
tinguished. The ringing lamp circuit is broken in the following manner. 
At the time the receiver is removed from the hook, a complete circuit may 
be traced from negative battery, through winding of relay D, out over 
sleeve side of line, returning on tip side of line through winding of relay 
C to positive battery. Energized by this current the lower make contacts 
on relay C close, furnishing a path for battery through the winding of re¬ 
lay E. Besides opening the lamp circuit, this relay when once pulled up, 
"Mil be seen to lock up, irrespective of any succeeding action of the relay 
C. 

Another important function is performed by the relay C, the current 
r rom the “East” exchange over the sleeve side of the trunk being switch¬ 
ed through the low resistance winding of the relay B instead of relay A, 
allowing sufficient current to flow r to extinguish the calling supervisory 
lamp at the “East” exchange. 

The two parties are now in a position to talk, the conversation being 
carried on through the repeating coil R, and each exchange furnishing 
the battery feed for its respective subscriber. The duty of supervision 
falls entirely to the “A” operator at the “East” exchange, and at the time 
No. 672 hangs up the receiver, relay C falls back to its normal position 
again switching the winding of relay A into circuit and lighting the 
“East” calling supervisory lamp. As usual when both supervisory lamps 
appear, the cords are taken down by the “A” operator and current ceases 
to flow through both relays A and B. The armatures of these two relays 
having returned to normal a circuit may be traced from negative battery, 
through the disconnect lamp, break contact of relay B„ make contact of 
relay D to positive battery, lighting the disconnect signal, and the trunk 
plug is returned to its seat. 

Should the “B” operator at the “West” exchange have received the 
“busy” test upon touching her trunk plug to the thimble of the multiple 
jack, instead of plugging in, the trunk plug would have been inserted in 
a jack known as the busy back. The peculiar noise from this circuit no¬ 
tifies both the subscriber and “A” operator that the desired line is busy. 

Fig. 484 shows the details of the busy back circuit, which contains 
an interrupter so arranged as to alternately make and break a battery 
circuit 22 times during approximately .17 of a second, and then holding 
the circuit broken for .057 s°cond. This machine is connected in series 
with a series o impedance coils and the primary ol a repeating coil; acioss 
the secondary of the coil, the busy back jacks are connected directly in 



380 


TELEPHONOLOGY 


parallel. On the sleeve side of the latter circuit an impedance coil is con¬ 
nected to positive battery, serving to light the disconnect lamp while the 
trunk plug remains in this jack. 

In exchanges where the busy back signal is required for trunking 
purposes, busy back jacks are also usually placed at the disposal of “A” 
operators, and the busy condition is never reported verbally to a subscrib¬ 
er. 

In Fig. 485, is illustrated the method of construction adopted by the 
Stromberg-Carlson Telephone Mfg. Company for its multiple switch¬ 
board sections of the so called nine panel type, the jack space for each sec¬ 
tion being divided into nine panels or three panels for each operator’s po¬ 
sition. This particular section as shown is practically ready for shipment 
from the factory, a portion of the iron frame and the greater part of the 
woodwork having been removed. As will be noted, the keyboard of each 
operator’s position is provided with 16 four party keys and thirty order 
wire buttons; each of the latter are so lettered as to indicate circuits to 
the toll board, chief operator’s, monitor’s and wire chief’s desks as well as 
neighboring exchanges. The manner of forming a hinge in the wires 
leading to the keyboard and of connecting the various keys and supervi¬ 



sory lamps is clearly shown on the keyboard to the right of the front view. 
The line, supervisory and ringing pilots for each position will be seen on 
the rail immediately above the keyboard. Directly over the supervisory 
pilot lamp may be noted an individually mounted jack and push button 
key, by means of which each operator is enabled to test the cord circuits 
in her position for open or short circuits. The operator’s jacks for each 
position are mounted in duplicate that monitors may assist on momen¬ 
tarily overloaded positions and to enable the relief operators beginning 
work before the relieved operators leave their positions. An extra oper¬ 
ator’s jack mounted at the extreme right of each section is provided for 
the use of the supervisory operator in answering the operator’s calls or 
information or assistance, which are indicated by an eight candle power 
signal lamp mounted above the top of the board every sixth section. 

In Fig. No. 486 may be seen the operator’s plug and jack in greater 
detail and also the style of breast plate transmitter, and receiver furnish¬ 
ed by this company. 

The method of mounting the supervisory relays on a hinged gate at 
the rear of each position is also to be noted, this practice providing the 
greatest degree of acessibility both for the relays, relay wiring, cords and 
terminal board connections. One section of this type of board has an ulti¬ 
mate capacity of 10,800 subscriber’s lines in the multiple space, 360 out¬ 
going trunk jacks and 630 answering jacks or 210 answering jacks per 













COMMON BATTERY EQUIPMENT 


381 


position, though it seldom occurs that the latter are all equipped. The an¬ 
swering jacks are mounted ten per strip, the type used in this board being 
shown in Fig. No. 487; directly above each answering jack and in the 
same mounting are seen the associated line lamp jacks, and also a line 



Fig. 485. 


lamp and various types of lamp caps, a number with markings as used for 
service designation. Tools for removing lamp caps and burnt out lamps 
may also be seen in the cut. 

The multiple jacks are of the same type as the answering, but mount¬ 
ed twenty per strip and separated into groups of five by white dots. Five 
strips of these jacks or 100 jacks are known as a bank, a thin white holly 



Fig. 486. 

strip attached to t^e top strip o p each bank separating the adjacent banks 
and by means of the number plates seen on the stile strips, Fig. 485, any 
bank may be readily located. 


























































382 


TELEPHONOLOGY 


The line and cut-off relays are quite similar in general design to 
those previously described in this company’s cord circuit, though each re¬ 
lay consists of but one spool, as shown in Fig. 488. 

The magnetic circuit of these relays is composed wholly of the best 
quality of Norway iron and in order to cut down so far as possible the re¬ 
luctance of the magnetic path, the end of the armature and the pivot piece 
from which it is suspended beneath the coil, are accurately milled and 
held firmly in contact by a stiff brass spring. At the front of the relay 
the armature normally rests upon the head of a small bolt extending up 
into the heel iron. When energized, the armature approaches the heel 



Rear of Jackstrip. Answering Jacks. Multiple Jacks. 

Fig. 487. 

iron, but metallic contact between the two is prevented by a small stir¬ 
rup slipped over the previously mentioned bolt and the heel iron. The ad¬ 
justment of the relay is also secured by means of this bolt into the heel 
iron, and by a lock nut above the latter. Motion is transmitted to the ger¬ 
man silver springs mounted on the brass bridge above the relay coil by 
means of a light brass yoke extending upward from the armature. The 
contacts, as usual, are of platinum rivets. 



Fig. 488. 

These relays are mounted on steel mounting strips, twenty line equip¬ 
ments per strip, each set of relays being protected as are all relays o the 
Stromberg-Carlson Company by aluminum casings. This type of casing, 
besides furnishing a perfect shield from magnet influence and dust, is ex¬ 
tremely light, sightly, and does not corrode. 











383 


COMMON BATTERY EQUIPMENT 


.. u” JV* 4 ? 9 is s J 10wn the Stromberg-Carlson four party key the action 
^ as been described in connection with the cord cicutt The key 

from thl r tee W h a , B T er Barff finish ' while the buttons reading away 
on fhil h £ a f re col ? re . ( [ respectively, blue, white and red. The springs 
k ^ contrary to the usual practice are mounted at right angles to 
the axis of the key and due to this construction the keys mav when re 

sible ’The^un^er of ? °chl than A has otherwise been found pos¬ 

sible. 1 he plunger of each key is provided with a key stop, which when 



Fi S- 489 - Fig. 489a. 


P i USh f a tUmbler extendin ^ the length of the key imme- 
b kGy i°Pv t0 one Slde ‘ When ful1 ^ depressed, and this key 

+k?\ h ?f pa ® sed beneath the tumbler, a spring at the end of the key throws 

™Llt? er b f? k mt ? the ? ormal Position, locking the plunger in the de- 
mpnt lS 0 Sltl f° n ‘-i other button which may be pushed at a later mo- 
momentarily throws the tumbler far enough to release the stop on 
a depressed key, the spiral spring restoring the released plunger to normal. 

er f a ^ s o thrown far enough by the cam when in the listening 
position to release the stop o any key plunger; the spring at the end of 
the key always returning the tumbler again to the normal position 



Fig. 490. 

The order wire keys as shown in Fig. 489a are also mounted on a steel 
mounting plate finished in Bower Barff, ten per strip, somewhat similar 
to the construction adopted for the four party key. 

The relays included in the ringing circuit for the purpose of lighting 
the ringing pilot lamps are necessarily of special design as they are ac¬ 
tuated by an alternating current of comparatively low frequency. The 
armature of such a relay must have sufficient inertia to hold the contacts 
closed while the energizing current and the magnetic flux pass through 
the zero value in changing direction and at the same time sufficiently sen¬ 
sitive to readily respond when ringing on the longest lines. This com- 























384 TELEPHONOLOGY 

pany has met the problem of a ringing relay in the form as shown by Fig. 
490. 

The armature of this relay is pivoted in a vertical position at the ex¬ 
treme end of and between two legs of soft Norway iron, which extend to 
the core at the rear of the coil. An insulated cam extends from the arm¬ 
ature through the upper leg and rests against a globular shaped depres¬ 
sion in the actuating contact spring above. The tension of the latter 
spring normally holds the armature thrown to one side o’ the core, but 
when the relay is energized, the armature is at once drawn over against 
the tension of this spring into the field of maximum magnetic flux, closing 
the contact above. 



Fig. 491. 

In Fig. No. 491 may be seen a regular section of the Stromberg-Carl- 
son Co.’s ten panel type switchboard as installed in the main office of the 
Kinloch Telephone Company, St. Louis, Mo. This style of section is de¬ 
signed for an ultimate of 17,000 lines in the multiple space, 840 outgoing 
trunk jacks multipled every seven panels, and 600 answering jacks. The 
type of jacks used on this style of switchboard is the same as already il¬ 
lustrated though necessarily mounted on somewhat closer centers. In or¬ 
der to bring so large a number of multiple jacks within the reach of one 
operator, the practice is adopted of lowering the plug shelf somewhat on 
this type of board, the key shelf being mounted on a slight angle sloping 
downward from the operator. 

































COMMON BATTERY EQUIPMENT 


385 


The “B” or trunking sections of this exchange are constructed on the 
same lines as the “A” board, but two operator’s positions, however, being 
equipped in each section. As no answering jacks appear in the “B” 
board, the multiple jacks are placed somewhat lower than the regular sec¬ 
tions. The front protection panels have been removed and keyboards 
opened on a “B” section in Fig. No. 491a, showing something of the inner 
construction. Figure No. 491b illustrates the rear of one of the regular 
sections. The regular multiple cables will be recognized near the top of the 
cut, with the outgoing trunk multiple directly below, while the answering 
cables are placed on evenly spaced wooden blocks on the floor of the sec¬ 
tion, allowing air to circulate freely around them. The answering cables, 
it will be seen, are covered by a false floor composed of removable trap 
doors. The rear curtains are composed of wood and roll up much the 
same as the cover of a roll top desk. 



Fig. 491a. 


As described in a preceding paragraph, all supervisory and miscel¬ 
laneous operator’s relays are mounted on swinging iron gates. Behind 
the relay gates are removable panels which expose the coids. 

Especial attention in boards of this size is devoted to protection 
against damage by fire. Each section is isolated from its neighbor )\ 
heavy sheet steel bulk heads, while within each section the multiple ca¬ 
bles are separated from the answering - cables by a fire proof scieen. A 
woodwork surrounding the cord and keyable compartment is also covere 

25 



































386 


TELEPHONOLOGY 


with a non-inflammable material, so that a fire originating at this point may 
not damage any other part of the system. 

A portion o" the St. Louis regular subscribers’ or “A” board is illus¬ 
trated in Fig. 492. This office at present contains thirty-seven regular 
sections equipped with 12,500 lines and ten “B” or trunking sections. The 
chief operator’s desk is placed at the head of the stairs, while a portion of 
the monitor’s desk, which at present consists of six positions, may be seen 
to the left of the stairway. 



Fig. 491b. 


The cabling on the St. Louis installation is also of interest, the gen¬ 
eral practice adopted by this company for connecting the main distribut¬ 
ing frame, intermediate distributing frame and relay rack being clearly 
shown in Fig. No.493; in this exchange, however, a line circuit slightly 
modified from that previously described was used, the relative position of 
the relay rack and intermediate frame being reversed. This practice re¬ 
quires a set of line relays to be permanently associated with each multiple 
line throughout the board, while the circuit we have shown requires a set 
only for each answering jack equipped, the total number of relays install¬ 
ed by the latter method often being considerably less than the multiple, 
or only the actual number of lines operated. In Fig. No. 493, the main 
frame is located at the left, the intermediate at the right, and the relay 
bays between. In another view of the same room, Fig. No. 494, the an¬ 
swering cables running to the intermediate frame may be seen at the up¬ 
per right hand corner, while slightly below and running across the view 
are the multiple cables, both from the regular and trunk boards. 























COMMON BATTERY EQUIPMENT 


387 



Fig. 492. 



Fig. 493. 

Fig. No. 495 illustrates the St. Louis Machine equipment and also 
the portion of the power board containing the fuse distribution panels. 


































388 


TELEPHONOLOGY 


The machine equipment, which is designed to carry the ultimate ca¬ 
pacity of the exchange consists of duplicate sets of Holtzer-Cabot motor- 
generator charging sets, and direct connected multi-cycle ringing genera¬ 
tors. The motors on the charging units both operate off of the direct cur¬ 
rent power circuit in the building, running at 800 revolutions per minute. 
The charging generators, each have a full load output of 500 amperes at 52 
volts. Each ringing unit consists of four generators, furnishing 16.66, 
33.33, 50.00 and 66.66 cycle current respectively, direct connected to a 
driving motor. To one end of each ringing unit’s shaft are also geared 
the usual howler and busy back attachments. One ringing set is driven 
from the building’s power circuit, while the other, for emergency use, is 
operated off the forty volt storage battery. Duplicate sets of storage 
batteries are also provided, each set consisting of 20 lead lined tanks with 
sufficient elements equipped to furnish at present a capacity of 2,720 am¬ 
pere hours or a total of 5,440 ampere hours for the exchange. This ca¬ 
pacity, it is estimated, is sufficient to operate the entire system, including, 
all desks and the toll board, for a period of 36 hours without recharging. 



Fig. 494. 


The circuits of the Multiple common battery switchboard urnished 
by The North Electric Co., are shown in Fig. 496. This circuit is typical 
of those where a double wound cord relay is used. 

The circuit is perfectly balanced, the supervisory relays Z and M are 
split wound and so connected as to feed battery to both sides of the lines 
through equally balanced windings, the cut-off relay E being in circuit 
with the third conductor of the multiple and cord. 

When the supervisory relays Z M are energized the supervisory lamp 
circuits are open and high resistance coils 20 and 42 substituted which 
permit only enough current to pass over the test sleeves of the jacks to 














COMMON BATTERY EQUIPMENT 389 

hold up the cut-off relays E, E 1 and maintain a busy test on the answering 
and multiple jacks. 

The supervisory relays being split-wound the circuit is adapted for 
use with common return or ground return lines. 

The only contacts introduced into the transmission circuit are the tip 
and ring contacts of the plugs with the jacks and those of the ringing 
key; the supervisory relay windings being connected directly to the tip 
and ring strands of the cords eliminates all relay contacts in the talking 
battery feed to the cords and lines. 

The relays are not required to work in parallel (the halves of the 
cord circuit being separated by condensers T and R) and there being no 
bridged coils the operation of all relays is very positive. 



Fig. 495. 


The operation is as follows: 

When subscriber A removes his receiver, current from battery passes 
through conductor 7, normally closed contact 5, conductors 3 and 1, sub¬ 
station set, conductors 2 and 4, normally closed contact 6, relay R, conduc¬ 
tor 10 to battery. Line relay F is energized, contact 9 closes and illumines 
line lamp G. The operator inserts answering plug H in answer¬ 
ing jack D, current then passes from battery through conductor 15, wind¬ 
ing S of relay Z, conductor 13, tip strand 11, tip of plug and jack, line 
conductor 1, substation A, line conductor 2, ring of jack and plug, ring 
strand 12, conductor 14, winding V of relay Z, conductor 16 to battery, 
thereby furnishing talking current to substation A. Relay Z operates to 
open contact 18 and close contact 17, thereby opening the circuit through 
answering supervisory lamp J, short circuiting coil 21 and establishing a 
circuit from battery th^ou^h cut-off relay F. conduc f OT" 8. sleeve of jack 
and plug, conductor 19, high resistance coil 20, conductor 24, contact 
























390 


TELEPHONOLOGY 


(now closed) 17, conductors 25 and 16 to battery. Relay E operates to 
open contacts 5 and 6, disconnecting relay F from the line, relay F is de¬ 
energized, contact 9 opens, extinguishing line lamp G. The operator con¬ 
nects her telephone set O by means of key K, takes the order, and tests by 
placing tip of calling plug I to the sleeve of multiple jack C'. If the line 
is disengaged, the sleeve of the jack and tip of the plug are of the same 
polarity (positive) and the operator’s receiver produces no click. If the 
line is engaged the sleeve of the jack is of negative polarity (being chang¬ 
ed from positive to negative by the sleeve of some other plug) and a busy 
click is produced in the operator’s receiver. Should the desired line be 
free, the operator inserts calling plug I in multiple jack C 1 establishing a 
circuit from ground through cut-off relay E 1 , conductor 8 1 , sleeves of 
jacks D 1 C 1 , third strand 41, supervisory lamp N and contact 37 in multi¬ 
ple with coils 42 and 43 in series, conductors 33 and 32, to negative bat- 



Fig. 496. 

tery. Cut-off relay E 1 operates to disconnect line relay F 1 from B‘s line. 
Upon insertion of plug 1 in jack C 1 , B’s line is rendered busy by changing 
the polarity of the jack sleeves from positive to negative (the third strand 
of the cord being of negative polarity). The operator then presses the 
ringing key K 1 which connects the ringing generator with B’s line. The 
generator may be either grounded or metallic. Until B removes his re¬ 
ceiver, supervisory relay M is not energized and lamp N remains illumin¬ 
ed. When B removes his receiver, current passes from battery through 
conductor 31, winding x of relay M, conductors 29 and 27, key K-K 1 , tip 
strand 39, tip of plug and jack, line circuit, ring of jack and plug, ring 
strand 40, key K'-K, conductors 28 and 30, winding y, conductor 32 to 
battery. Relay M operates, first to open contact 37 thereby extinguishing 
lamp N and second to close contact 36 short circuiting coil 43 and allow¬ 
ing the high resistance coil 42 to remain in the third strand circuit. When 






























































391 


COMMON BATTERY EQUIPMENT 

either substation receiver is replaced the corresponding supervisory relay 
operates to close its normally closed contact (18 answering, 37 calling) 
and the supervisory lamp is illumined. With the answering supervisory 
relays Z, one spring ot contact 18 is commoned and connected to supervi¬ 
sory pilot relay L. When lamp J is illumined, relay L operates to illu¬ 
mine supervisory pilot lamp Q. The removal of the plugs restores all 
parts to normal and lamps J. N and Q are extinguished. 



The common battery circuit used by the Kellogg Switchboard and 
Supply Co., is shown in Fig. 497. Two batteries are shown as supplying 
energy to the cord circuits, but one battery may be used if desired. The 
operation of this circuit is described by W. S. Henry in the American 
Electrician, as follows: 

“When the receiver rests on the hook the condenser in the subscrib¬ 
er’s instrument prevents the flow of battery current through the subscrib¬ 
er’s telephone; but when the receiver is taken off the hook, sufficient cur¬ 
rent flows from battery -j- B ' through g — g' — T — I —line relay LR — B' to 
cause LR to attract its armature, thus causing the line lamp, L, to light. 
The operator replies by inserting the answering plug, AP, in the proper 
jack and closing the listening key. 

“Current will flow from B through g —cut-off relay, CO — sleeve side 
of circuit—relay SA back to B, which causes the 500-ohm cut-off relay CO 
to attract its armature, thereby cutting out the line relay, LR, which in 
turn extinguishes the line lamp and also connects the two-line wires to 
the jack. Current can now flow and close both the supervisory relays, SA 
and ST, because the line circuit is closed at the subscriber’s instrument. 
The closing o the relay, ST, opens the circuit through the answering su- 




















































































392 


TELEPHONOLOGY 


pervisory lamp, AL, and thus prevents the lighting of the latter at this 
time. The operator can now communicate with the subscriber. The ope¬ 
rator’s receiver and a condenser are connected in series across the cord 
conductors, but there is also a condenser, CC, in each cord conductor be¬ 
tween the operator’s head set and the subscriber’s line circuit. 

“The operator proceeds to complete the connection by touching the 
tip of the calling plug, CP, to sleeve, s, of the jack belonging to the line 
wanted. If the line is busy, due to a plug being in a jack of that line at 
some other section, a click will be produced in the operator’s receiver in 
the following manner: Current flowing from a battery through a 100- 
ohm relay — sleeve side of some cord circuit — sleeve, s — tip t' of calling 
plug — a — 5,000-ohm test relay, R, to ground, causes R to close its cir¬ 
cuit, which short-circuits the impedance coil, /", thus producing a sharp 
increase in the current through the primary, p, which causes a click in the 
operator’s receiver. The operator then informs the waiting subscriber 
that the line called for is busy. If the line is not busy, s, as well as V will 
be at the same potential as the ground; relay LR will not be affected and no 
click will be produced. If the line is not busy, the operator inserts the plug 
in the jack, which will operate the cut-off relay CO'. She then opens her 
listening key and closes her ringing key. 

“Current now flows from B' through the ground — cut-off relay, CO' 
— sleeves, s, of jack and plug 1 — resistance, r, back to battery, thus hold¬ 
ing the cut-off relay closed while the ringing current flows from the gen¬ 
erator through the tip side of the line—subscriber’s bell and condenser— 
sleeve side of line—resistance, r — battery B' — ground to generator. 
When the ringing key is released, current flows from B' through ground 
—cut-off relay, CO' —sleeve, s, of jack and plug—relay, SC —back to bat¬ 
tery, which keeps both relays, CO' and SC, closed.. The closing of SC 
causes current to flow from B' through ground — e — calling supervisory 
lamp, CL (which it causes to light) to battery. The lamp, CL, will re¬ 
main lighted until the subscriber called takes his receiver off the hook. 
Current can then flow from B' through relay, TC — V —tip side of line— 
subscriber’s transmitter and impedance coil—sleeve side of line —s —re¬ 
lay, SC —back to battery. This causes the relay TC to close, thus opening 
the circuit through the calling supervisory lamp CL, which is an indi¬ 
cation to the operator that the called subscriber has answered his tele¬ 
phone call. All three relays— CO, SC, TC —are now' energized, and the 
condition of the circuit while the two subscribers are holding a conversa¬ 
tion is shown at (a). 

“It will be seen from this diagram that each subscriber’s circuit is 
supplied with current from a separate battery, there being a 100-ohm re¬ 
lay, which also acts as an impedance coil, between each terminal of each 
battery and the line wires. The battery and one of these relays on each 
side of the cord circuit are shunted by a 500-ohm cut-off relay whose re¬ 
sistance is sufficiently high not to deprive the line circuit of all the cur¬ 
rent necessary for the operation of the transmitters, and yet not too high 
to cause this 100-ohm relay to open when the receiver rests on the book 
switch. 

• ..! .1’ b. T 

“As stated, each subscriber’s transmitter receives current from a sep¬ 
arate battery through two inductive resistances, that is, relays. A fluctu¬ 
ation of current in the original subscriber’s circuit produces a similar 
fluctuating difference of potential between points, x y, which will produce 
a fluctuating flow of current through the called subscriber’s circuit. 


COMMON BATTERY EQUIPMENT 


393 


“When the subscribers hang up their receivers, the supervisory re¬ 
lays, TA and TC, are deprived of current and hence release their arma¬ 
tures, which cause the supervisory lamps, AL and CL, to light, thus noti¬ 
fying the operator that she should pull out the plugs, which restores the 
circuit to its normal condition.” 

Another form of busy test from that just described is also used with 
this system. The test relay, instead of short circuiting the impedance 
coil in the primary circuit of the operator’s set, is arranged to put battery 
on a third winding on the induction coil; this by induction gives the busy 
test as previously described. 

The trunking circuit used by the Kellogg Company is shown in Fig. 
498. The jack on the right is located on the A operator’s position or the 
one at which the call originates. The rest of the equipment is located at 
the B operator’s position or the one at which the call terminates. This 
latter may even be another exchange, several miles from the A or origi¬ 
nating position. 

The trunk jacks may be multiplied throughout the A exchange, same 
as the regular subscriber’s jacks, so that every operator may have access 
thereto. 



Fig. 498. 


If a subscriber calls in at exchange A and wants a subscriber who is 
connected with exchange B the operator at exchange A^ who receives the 
call pushes her order wire button which is marked B . The wire from 
the “B” order wire button terminates at the head telephone of one of the 
incoming trunk operators at exchange B. The operator at exchange A 
then tells the incoming trunk operator at B over the order wire circuit 
what subscriber at B exchange is wanted. The B exchange incoming 
trunk operator tells the A exchange operator which trunk to use. the A 
operator then plugs into the corresponding out-going trunk jack in .her 
section. This puts battery on the sleeves of all the jacks connected to the 
trunk, and makes same “busy”, so that no other A operator will useit e 
trunk, winch might otherwise happen, through an eiior in understanding 
the trunk assigned. 































































































394 


TELEPHONOLOGY 


Battery now flows over the trunk from the A operator’s cord circuit, 
and operates relay R 1 at the B board, which pulls up its armature. The 
purpose of this relay is explained later. 

The resistance of this relay (15,000 ohms) is so great that the super¬ 
visory relay in the calling cord of the A operator’s position is not operated 
until this 15,000 ohm relay is short circuited by relay R 2 as will be de¬ 
scribed. 

The B operator tests the line called for with the trunk plug. The 
test circuit is shown from the armature of relay R 3 , through test relay 
and 3rd., winding of induction coil. If the line being tested is busy, the 
test relay will be operated, because battery will flow from the sleeve of the 
busy line through test relay to ground. This causes test relay to close, 
and battery flows through the 3rd., winding of the induction coil, causing 
a click in the operator’s receiver. This being the case the B operator puts 
the trunk plug into the jack marked “busy back’’ and a peculiar signal or 
tone is transmitted to the A operator on the trunk, notifying her the line 
is busy. Plugging into this jack will also flash the supervisory lamp in 
front of the A operator by operating R 2 and thereby alternately cutting 
R 1 in and out of circuit, thus giving a visual as well as audible signal to 
the A operator. 

If the wanted line is not busy, the operator plugs in same and rings, 
the cut-off relay of this line is operated in the usual manner and trunk re¬ 
lay R is also operated as it is in series with the cut-off relay. When the 
subscriber answers, relay R 2 is operated, this closes a pair of contacts 
which short-circuit R 1 , and remove it from the repeating coil circuit, this 
coil separating the incoming battery from the A operator, from the B bat¬ 
tery, while providing a path for the voice currents. 

If the A operator plugs into the jack of the designated trunk line be¬ 
fore the trunk operator at the B exchange inserts the corresponding trunk 
plug into the jack of the called line, or if the A exchange operator plugs 
into a jack other than that of the trunk assigned, the disconnect lamp as¬ 
sociated with the correct or incorrect trunk at the B exchange will light, 
thus serving as a guard against inaccurate connections. However, as 
soon as the trunk plug has been inserted in the multiple jack, the discon¬ 
nect lamp will be extinguished, in case it has been lighted, and the ringing 
lamp will light. This lamp remains lighted until the subscriber removes 
his telephone from its hook. 

If the operator plugs into the trunk before the B operator puts up the 
plug, the disc, lamp will light because it will be grounded by contact X of 
relay R 1 , this ground being derived from the back contact of relay R 3 . 
When R 3 is operated, this contact is broken and the disc, lamp extin¬ 
guished. 

Supposing the B operator puts up the plug before the A operator 
plugs into trunk jack, then the disc, lamp will light because ground is ap¬ 
plied to the lamp through relay R 3 to armature of relay R 2 , and bottom 
contact of R 1 . As soon as R 1 is operated by the A operator plugging into 
the jack the disc, lamp is extinguished. 

The ringing lamp will remain lighted, after the plug is in a jack until 
the party answers and thereby energizes R 2 , which energizes relay R 4 
which cuts the battery off the ringing lamp, this is really the local super¬ 
visory signal. 

The operation of the “Don’t Answer” jack is similar to “Busy Back” 


COMMON BATTERY EQUIPMENT 


395 


previously described. The operation of the pilot lamp connected to the 
trunk disc, lamps will be readily understood by reference to the figure. 

Fig. 498 also shows the arrangement of the pilot and night alarm cir¬ 
cuits used with this switchboard. 

When the subscriber at the B exchange replaces his telephone upon 
its hook, the calling lamp at the A exchange will light as R 2 opens, thus in¬ 
serting the resistance of R 1 in the A cord circuit and the A operator—the 
“A” subscriber having also hung up his receiver—will remove the connec¬ 
tion. The act of removing the calling plug from the outgoing trunk jack 
at the A exchange will light the disconnect lamp at the B exchange by al¬ 
lowing R 1 to open and the B operator will then take down the connection. 

The common battery system furnished by the Vote-Berger Co., is 
unique in so much as no relays are used, either in the line or cord circuits. 

For reasons which have been previously discussed, it is impractical 
to place the line lamp directly in circuit w r ith the line battery, therefore 
relays are used in all systems but this, to actuate the lamp, which is placed 
in a local circuit. To eliminate these was the problem. The solution of 
this problem was found in the use of iron wire ballast. Iron wire ballast 
had been used for years in power work and in conjunction v/ith the Nernst 
lamp. The action in conjunction with the Nernst lamp came the nearest 
to fulfilling telephone conditions, and deserves some little consideration. 
An iron wire of .002 inch in diameter is placed in series with the filament 
of a salt of a rare metal used in the Nernst lamp to protect this filament 
from fluctuations in voltage. The filament which is used is extremely 
sensitive to slight variations in current. It has a negative co-efficient 
which has an extremely sharp curve at the point of best illumination. If 
placed on a power circuit without precaution a slight increase of voltage 
will cause an increment of current to be r orced through the filament. 
This reduces the resistance of the filament, which will again allow more 
current to pass through. The result is that a variation of one and a half 
volts on a one hundred and ten volt circuit will burn out a Nernst lamp 
instantaneously unless the filament is protected. After a great deal of ex¬ 
perimenting, the ballast already mentioned was designed and found to 
protect absolutely this extremely sensitive filament. As used by the 
Nernst Lamp Company, the iron wire is spiraled and held between por¬ 
celain discs, the whole beinq sealed in a glass bulb filled with hydrogen 
gas. For the purposes of the Nernst lamps, this ballast seems to leave 
nothing to be desired. With a variation of less than 10 per cent in cur¬ 
rent, the resistance of the ballast is increased or decreased 100 per cent, 
which will fully protect the illuminating filament. 

When it was attempted to apply this same ballast to a telephone line, 
it was found that it failed for two reasons. First, the iron wire, on ac¬ 
count of the presence of the hydrogen gas, radiated the heat so quickly 
that a current of .04 of an ampere was needed to heat it to a sufficient; 
temperature for illumination. It is, of course, impracticable to send such 
a current out over a subscriber’s line and impracticable to use such a cur¬ 
rent in a subscriber’s lamp. The second reason for failure of this type of 
ballast was that a variation of 100 per cent was found to be insufficient 
to take care of the varying lengths of subscribers’ lines. It was thought 
at first that this 100 per cent range could be easily increased by heating 
the wire to a higher temperature if the first objection could be overcome. 
Fxperiment proved, however, that when a ballast of this tvpe was heated 
to a higher temperature than it was designed to withstand, the wire be- 



396 


TELEPHONOLOGY 


came soft and the light spiral coils would collapse and pull apart from 
their own weight. 

After considerable time was spent in both theoretical and practical 
investigation, it was found that if a wire .001 of an inch in diameter were 
sealed in a vacuum, it could be brought to the operating point by .07 of an 
ampere, which is normal current for a telephone signal lamp. Also, it 
was established that this current is easily sent over subscribers’ lines o: 
any practical length. 

The next question to be solved was a means of mounting this wire so 
as to allow it to be heated to a high temperature, thus giving a greater 
range of variation of resistance. This was the hardest part of the prob¬ 
lem, and was finally solved by the design of a ballast mount, as illustrated 
in Fig. 499. The inner tube of the ballast has a deep thread cut into the 
glass. The bottom and sides of this thread are purposely roughened. The 
fine iron wire is then wound in the thread and the whole sealed in the out¬ 
er blub, in which a vacuum is maintained. With a ballast of this style the 
wire is supported throughout its whole length, but on account of the 



Fig. 499. 

roughness of the thread does not lie in intimate contact with the glass. In 
such a ballast the wire may be heated to so high a temperature that it be¬ 
comes red and soft. The only result is that it droops down against the 
sides of the thread and remains thus supported. It is impossible for it to 
break of its own weight, as is the case with the Nernst type of ballast. 
After the perfecting of this piece of apparatus, it was found that a ballast 
was obtained that would give a variation of 1,000 per cent in its resistance 
with very slight increase of current. This, of course, is more than is 
needed to offset the variation between the resistance of any practical tele¬ 
phone lines to subscribers’ stations. With the question of the ballast 
solved, the line circuit was complete. The ballast line lamp, subscriber’s 
line and power are all placed in series, as shown in Fig. 500. The ballasts 
for all subscribers’ lines are exactly alike, no difference being made in 
long or short lines. The voltage of the battery is such that on a long line 
the current sent over the subscriber’s line is sufficient to illuminate the 
line lamp. In this instance the ballast remains cold. When the ballast is 
in a subscriber’s line of zero, or approximately zero resistance, the incre¬ 
ment of current that is added on account of the difference in resistance of 
the lines is sufficient to increase the resistance of the line ballast approxi¬ 
mately 700 per cent. On all commercial lengths of lines this means that 
the line lamp gets practically the same current, whether the subscriber’s 
telephone is located in the exchange building or several miles distant. 

The cord circuit without relays was somewhat more difficult to de¬ 
sign. The final design however was very simple. When an operator’s plug 




COMMON BATTERY EQUIPMENT 397 

is inserted in a line jack, and the subscriber’s telephone is removed from 
the hook, we have battery flowing through the cord to the subscriber’s 
telephone and jack. If we place across this cord a signal lamp and an im¬ 
pedance coil to prevent the loss of voice currents, and design the resis¬ 
tance of the battery teed coils, the resistance of the lamp, and impedance 
correctly, it is evident that the subscriber’s line loop will form a shunt on 
the supervisory lamp. If this supervisory lamp circuit is of sufficiently 
high resistance, it is evident that the resistance of the longest subscriber’s 

ln P lac ^ 1 ^ a ^ use be low enough to shunt out the supervisory lamp. 
When the subscriber’s telephone is hung upon the hook the shunt is re¬ 
moved and the lamp receives its full current, giving the disconnect signal. 

A combination of this circuit with the line circuit already described 
gives a switchboard of great simplicity. It will be seen that there are no 
moving parts anywhere in the system, and no contacts except where the 
signal lamp is cut off at the jack by the insertion of the plug. For large 
exchange work, where a multiple is desired, the line circuit has been so 
modified in conjunction with the cord circuit that these contacts are done 
away with. In the largtr boards there are no contacts except between the 
tip and ring of the plug and tip spring and ring spring of the jack. 

The line and cord circuit is shown in Fig. 500 and the operation is as 
follows: Subscriber A desires to talk with subscriber B. A removes his 
telephone and battery flows through the following circuit: Positive side 
of battery flows through the contact of jack to subscriber’s line, through 
subscriber’s instrument back on the second side of line to the second cut¬ 
off contact of jack through line signal lamp, through line ballast to battery. 



Fig. 500. 


Now the operator, seeing the illumination of the line lamp, places the 
answering plug in the jack corresponding to subscriber A’s line. The in¬ 
sertion o ' the plug lifts the tip and ring spring from the cut-off contacts, 
hence removes battery lamp and ballast from the line. Battery for the 
subscriber’s transmitter then flows from grounded side of battery 
through impedance coil A. through the key contacts, through the tip of 
the plug, tip spring of jack, subscriber’s line, subscriber's instrument, sec¬ 
ond side of subscriber’s lire, to ring spring of jack, ring of plug, contact 
of key and impedance coil B to battery. The supervisory lamp, which is 
permanently attached to the tip of the plug, is connected through the im¬ 
pedance coil C to the sleeve of the plug. When the plug is inserted in the 
jack the sleeve of the plug is connected to the ring by the wire D in the 
line jack. Asa subscriber’s instrument shunts this supervisory lamp and 
impedance coil, the lamp is dark. The operator learns by;inquiry that 
subscriber A desires to communicate with subscriber B and inserts the 
connecting pluo- into the line jack corresponding to the line of subscriber 
B and rings. Until B answers, we have batttery flowing from grounded 













































398 


TELEPHONOLOGY 


battery through impedance coil A', through key contact, tip of plu 0 ', 
through supervisory lamp, impedance coil C', sleeve of plug, sleeve of 
jack, ring spring of jack to ring of plug through contact of key impedance 
coil B' to battery. As this supervisory lamp has no shunt, it is illuminat¬ 
ed, and when subscriber B takes his telephone from the hook and answers 
to the ring, the resistance of his line, including his set, shunts out the su¬ 
pervisory lamp. Both lamps then remain dark until the subscribers are 
through talking, when each lamp will be illuminated by the act of the sub¬ 
scribers hanging up their telephones, which removes the shunts from the 
corresponding supervisory signals, giving a disconnect signal to the 
operator. 



A circuit using only one relay per line, and no relays in the cord 
equipment, is shown in Fig. 501. Battery passes to each line through 
windings 1 and 2 of relay B which serves ps an impedance coil, preventing 
talking currents from passing from the lines into the battery. When a 
subscriber removes the receiver from the hook, relay B is energized and 
draws up its armature, lighting the lamp E, through resistance C. 

*“Upon the operator answering the call, she picks up the plug G and 
inserts it into the spring jack F. Upon examining the calling circuit, it 
will be observed that the ring of the plug is connected to the lamp H, and 
that this lamp is connected to the plus side of the battery, and that the 
line lamp E is connected to the same side of the battery. 

“Now, assuming that the armaure of the relay B is in its upward 
position and the plug G placed into the spring jack F, the lamp H is shown 
connected in parallel with the lamp E. If it is considered that the lamp H 
is of a much greater capacity; that is, that it requires more current to 
light it than the lamp E, and that the resistance C permits the passing of 
only ehough current to light the E lamp, it is obvious that the H lamp, 
with its large current requirements and connected in parallel with the E 
lamp, takes enough current away from the E lamp "or practically extin¬ 
guishing it, but owing to the limiting of the current supply available 

* Telephone Magazine. 


































































399 


COMMON BATTERY EQUIPMENT 

% 

through the C resistance the H lamp will not produce a signal. The mo¬ 
ment, however, that the subscriber hangs up his receiver, it results in de¬ 
energizing the B relay and this permits of the armature connecting to the 
C resistance coil and ring of jack F falling back upon a contact to which is 
connected the D resistance, which is similar to the C resistance, dilfering 
from it, however, in the respect that it is of a somewhat higher resistance. 
The moment that the armature falls back the lamp E is, of course, cut out 
of circuit and the combined parallel resistance o^ C and D is low enough 
for permitting the lamp H to receive a sufficient amount of current for 
lighting it. Upon the operator observing the clearing signal, the plug 
would, of course, be withdrawn and no change take place in the line cir¬ 
cuit other than cessation of the current passing through the resistance C 
and D. 

“The tip and sleeve circuits of the answering and calling plugs are 
connected together directly through condensers K and L.” 

While this system possesses the merit of great simplicity, it also pos¬ 
sesses the disadvantages of no pilot or night bell circuits, and in order 
to permit the use of these, it is customary to furnish a second relay, wired 
in the sleeve conductor in such a manner that when a plug is inserted in 
a jack, this relay is operated and opens the line circuit. This arrange¬ 
ment is shown in Fig. 502. When the subscriber signals, the line relay 
closes contact a, putting a ground on contact c and lighting line lamp 
through pilot relay which also operates, lighting the pilot lamp. When 
the operator plugs in battery current passes through the supervisory lamp 
H Fig. 501, to the sleeve of jack, and through the cut off relay which opens 
contact c, and extinguishes the line, and pilot lamps. The cord lamp H 
is not illuminated, owing to the high resistance of the cut-off relay, which 
is usually 500 ohms, this being in series with the lamp. 



When the subscriber han^s up, the line relay falls back, thereby 
closing contact b. This short-cicuits the high resistance, cut-off relay, 
and sufficient current now passes through resistance C to light the supei- 
visory lamp. 

Another circuit using only one relay per line, and operating on a com¬ 
bination of the impedance coil and representing coil principles, is shown 
in Fig. No. 502b. When the subscriber calls relay L draws up its arma¬ 
ture, lighting lamp M. Upon the insertion of a plug the jack thimbles N 
and O are short-circuited thereby extinguishing lamp. The supervisory 
lamp P is now in circuit but is not illuminated, owing to the Resistance Q 
which is in shunt with the cord lamp as long as relay L is energized. 
When the subscriber han o s up and relay L opens its contact, battery nows 
through the cord lamp and resistance Q, and the lamp is illuminated. 


















































400 


TELEPHONOLOGY 


It would seem that the line relay windings could be given a high 
resistance, and the talking battery fed through the repeating coil in the 
cord circuit, or like the system shown in Fig. 501, battery could be fed 
through the line relay and the cord circuit consist of two condensers or a 
repeating coil with condensers between the centre terminals. 

The preceding brief descriptions of some systems in common use, 
will serve to demonstrate that many different circuit combinations are 
possible; to describe each one in detail would be almost impossible, nor is 
this necessary, for a thorough understanding of any one system, will en¬ 
able one to become familiar with any other after a short experience there¬ 
with. 

The system in most general use, is probably that used by the various 
licensee companies of the American Bell Telephone Co. This apparatus 
is furnished by The Western Electric Co., who have developed this line of 
equipment to a high degree of perfection. As this system is in such 
extended use, a detailed description of the apparatus may be of interest, 
as there is hardly a large city in this country which is not equipped with 
some of this apparatus. 

The general characteristics o? this system have been referred to, and 
shown in Fig. 475. A later line circuit is shown in Fig. 503. The first 
difference between this and the older circuit is the double wound line 
relay, each winding 1,000 ohms. This high resistance materially reduces 
the amount of battery necessary, and also eliminates the loud click in the 
ear present in the older system when the receiver hook is moved up or down 
or when the operator plugged in, as when answering the call. 



Fig. 503 shows the arrangement of the equipment, the wiring through 
main and intermediate frames, etc. The connections of the multiple and 
answering cables in the intermediate frame are such, that when looking 
at the frame on the answering jack side, the first or outside clip is the tip, 
next the ring, then sleeve and lamp wire. Three conductor or “triple'’ 
jumper wire is used to connect the answering and multiple jack sides of 
the frame, the usual colors being red, white and blue, the tip being white, 
ring blue and sleeve red. This color scheme is also used for the plug cord 
conductors. 

Fig. 503a shows the line and cut-off relay, these being mounted 
together. A mounting plate holding ten of these units is usually provided. 
The top relay in the figure is the line relay, the bottom the cut-off. 




































COMMON BATTERY EQUIPMENT 


401 



talking wires be paired, or cross talk would result. 



Fig. 503a. 


The multiple cables contain 63 wires each, twenty pairs, twenty 
singles and one spare pair and single. Each pair and single has a distin¬ 
guishing color of insulation to enable them to be easily located. 

The answering jack cables are similar to the multiple, except they 
may consist of 83 wires, twenty pairs for talking and twenty pairs, one 
wire of each for the sleeve and one for the lamp. The plain or solid color 
wires of the pairs usually connect to the tips, the code or colored wires to 
the rings, and the single wires to the sleeves. 



Fig. 503b. 


The majority of troubles with the line circuit are due to careless 
soldering in the frames and at the jack terminals. The greatest care 
should be taken to secure perfect connections and when working in the 
multiple, after replacing a jack strip, carefully examine all terminals to 
see that no wires are broken or no jack spring ends in contact. 

Sometimes an open wire occurs in the multiple. This is easily loca¬ 
ted by connecting a line lamp to the tip and ring o ' a plug. Start at the 
last multiple and plug in, the lamp will not light until the break has been 
passed, and when this occurs, the break will be found between the point 
tested and the last point, usually at a jack spring. 

An open sleeve is denoted when it is impossible to put out the line 
lamp by plugging into the jack, this being located by plugging in each 
multiple jack. It is usually due to a broken wire or, rarely, by an open 
cut-off relay. 

Short circuits in the multiple are often caused by lead pencil points, 
due to the operator having a pencil in her hand when answering a call, 
and sticking the point in a jack, breaking the point off. These “shorts’’ 










402 TELEPHONOLOGY 

can usually be distinguished from others, by their causing the line lamp to 
flash, or burn intermittently. 



Fig. 503c. Fig. 503f. 

Often pieces of solder become lodged between the terminals on the 
frames, or a jumper wire is pulled too tight, thereby causing two termi¬ 
nals to close together. The frame terminals are close together as shown 
in Fig. 503c and care must be exercised when making connections. The 
same applies to jack strip connections. As shown in Fig. 503d, the jacks 
are mounted very close together and neat work is imperative when sold¬ 
ering the wires thereto. 



Fig. 503d. 


Fig. 503e shows the cord circuit. The repeating coil used in the older 
installations is of the type shown in Fig. 503f. 



Fig. 503e. 


This coil has a core about 1/2 in. diameter and 7 in. long. The wind¬ 
ing spaces are about 3 in. long, a head being placed in the middle. The 
windings vary in resistance depending upon the type of coil, from 45 to 
22 ohms. The wire is 26 or 28 cotton covered, from 1,800 to 3,000 turns 
on each winding. In each space is put two windings, the wire run on side 
by side. Each end is wound in the reverse direction from the other, so 
that w T hen the coil is connected in circuit, the windings are in relation to 
the core and each other as shown in Fig. 503g, from which it will be seen 
that a non-inductive relation exists between the windings connecting to 
each cord, and voice currents meet no opposition to circulating in this 
path, while the coil as a whole offers great opposition to voice currents 


































COMMON BATTERY EQUIPMENT 403 

that may try to flow outwardly from one coil through another. The core 
is made large and of fine iron wire, so that these stray impulses may be 
killed, and in addition, the coils are encased in a heavy iron tube, so that 
they may be mounted side by side without danger of cross-talk. 


CALL, nui s. 


A/V£> PLOCx. 


GG 


ours/pe- s/v pp - 

7 • 7/Vi>l&£- £/VPi* - 
£>//<£ CT/O/V 

or /rwD/A/ 6 . 





'22 /OLTP- 


o 


7 acm yrp'6. = oxsifr 
trpo's. */- 4/roc//vp 
rone- - &y «s /pe-, 

*3-2~fAstr A3-/-4- 
" TACH W6 -2000 TURKS - 


Fig. 503g. 


Trouble seldom develops in the repeating coil. The arangements of 
the terminals on different types is sometimes confusing. Some of the 
terminal arrangements will be observed 'rom Fig. 503h, which also shows 
some of the combinations possible with these coils. 


'jar 

*0 co«© 



0 

l 

t 

m • 1 

» 

i 

1 







-4 

MtouwPl 


«0.iVA GOU. 

•s ubto on »c*»cu» 


ill 
• ! 

tj l(j 

"f •! r 


* ‘ ! *k 

•p »«vco«o 

f I 

\ -^T 

co«o 

»»»«•• 

' , '' M »•< a*’ 

-QBUB -r- 

SBC Q 

, 'UM 

-rSK25J£) 


•*>.'3 6 CQk > 3-0 *U*LATmO COi 

ASU3LOON CO*OCWCU*T »SU«0 0<lTaw•^C'•CW , 

F'g- 



f C 10*0 





i 

t j 

1 

u 

n 

i 

ir 









•ov-c hpiatiwg co.» 

•5 OS<0 On r» u o> C'»C 


*• IlLKN 

tKMwWI 

j 

Mint* 


; 

— 



10 tVA-*t*iA7»C CO.V. 
uMOQN W)*0C‘*O»i 


P'H 


Fig. 503h. 


A later type of coil is shown in Fig. 503i. Here the windings are of 
23 ohms resistance wound on a ring core of soft iron wires, the whole 
being encased in a heavy iron shield filled with rosin, in operation these 
are the same as the coils previously described. It is customary to put 
two of these coils on the same base, to facilitate mounting in the standard 
coil rack. 



Fig. 503i. Fig. 503j. 


The next important part is the supervisory relay, as shown in Fig. 
503j. This has a % in. core, and winding space 1% inches. The copper 
winding measures about 21 ohms and consists of 1,800 turns of 28 silk 
covered wire. As this relay is in series with the talking circuit, this num¬ 
ber of turns would have considerable impedance, therefore about 15 feet 
of 30 gau~p German silver wire, bavin? a resistance of about 31 ohms is 
doubled and placed over the copper winding and connected across same. 




































































































404 


TELEPHONOLOGY 


This gives the relay a total resistance of only 12.5 ohms, and makes it 
entirely non-inductive. 

The adjustment of this relay is an important factor in the successful 
operation of this system, therefore special means for testing same is pro¬ 
vided. It is customary to wire two jacks in each section, usually the 0 and 
600 jacks (these being at the extreme ends of the average multiple) to the 
test equipment, also a jack midway between these, for instance No. 300. 



Fig. 503k 


The test is made as follows, referring to Fig. 503k. The portable 
test board equipped with two strap keys and a plug as shown, and the plug- 
inserted in 300 jack as shown. The cord containing the relay under test 
is put in jack 0 or 600 whichever is nearest. This should light the super¬ 
visory lamp, owing to the ground on sleeve of test jacks, the resistance R 
corresponding to a cut-off relay. It will be seen that a resistance of 10,000 
ohms is now across the cord, and the supervisory relay should not operate 
as this is a high limit, set to allow for leaky lines, etc. 

The key marked T is now depressed, and 8,800 ohms of this resistance 
cut out. The supervisory relay should now operate, putting out the cord 
lamp. The relay should release and light the lamp when key T is released 
and should be adjusted accordingly. 

If the relay does not release when the key is released there is danger 
of the relay sticking on a leaky or low resistance line, and no supervision 
would result. 

The key marked S is now depressed, and all the resistance is cut out, 
except 100 ohms. The relay now gets the full battery pressure and should 
work freely and not freeze. 100 ohms is taken as representing the least 
possible resistance the relay will ever work through, this about represent¬ 
ing the heat coils and subscriber’s set, on a line of no resistance. 

In adjusting this relay care should be taken to use the special 
wrenches provided for the purpose, and to adjust so that the relay is not 
sluggish in action. A little practice and observation will enable rapid and 
accurate adjustments to be made. 

To test for “cut outs” or broken cords, put plug in test jack and 
depress S key, listen with operator’s receiver while shaking the cord and 
the defect will manifest itself by the usual scratching or scraping 
sound. 

Sometimes the cords will burn from various causes. Some of these 
are shown in Fig. 5031, and are as follows, referring to the numbers in 
the figure. 














































COMMON BATTERY EQUIPMENT 405 

(1) Heavy fuse at D. 40 w coil C connected at B instead of A. 40 to 
coil C short-circuited. Res. coil or relay E short-circuited. 

(2) Heavy fuse at D 40 w coil C connected at B instead of A. 40 w 
coil C short-circuited. Plug seat at E grounded on frame of switchboard. 
Tip and ring crossed at F. 

(3) Armature A grounded on mounting plate. Tip and ring short 
circuited at B. Sleeve of jack crossed with battery at C. 

(4) Service meter key at A sticks, resistance coil B short-circuited 
(or key sticks, plug seat grounded.) 




2 . - £ Mt/X IM* 


♦I / 






vr 

E 


T 

I 



Fig. 5031. 


The next piece of equipment is the 40-83 ohm resistance in the sleeve 
of the cord. This is shown in Fig. 503m. It consists of a winding of Ger¬ 
man silver wire on a flat mica mounting, re-inforced with a brass frame. 
A centre terminal not shown in the figure brings out the tap between the 
two parts. This resistance sometimes becomes open, which can be easily 
tested for by putting one side of a receiver to ground, and applying the 
other side to first one t^minal or the other of the coil the open side will 
be the one where no click results. 



Fig. 503m. Fig. 503n. 


The lamps used in the cord circuits are adapted to 12 volts. In 
appearance they are similar to the line lamps, except usually the filament 
consists of a single turn instead of two laps. The lamp is shown in 
Fig. 503n. 

The cords and plugs are similar to those used in magneto systems. 
A Western Electric cord is shown in Fie-. 503o, and repairs should be 
made to these as explained in connection with Fig. 183. 

The operators’ circuit is shown in Fig. 503p. The transmitter and 
receiver are of the same general description as those used in magneto 
systems. The induction coil is of peculiar construction, and really con¬ 
sists of two coils, mounted side by side, as shown in Fig. 503q. Each 
spool has a 18 ohm primary and a 145 ohm secondary. A non-inductive 



























































406 


TELEPHONOLOGY 


resistance of 350 ohms is wrapped around one of the coils, and the receiver 
is so connected that it is in a bridge composed on one side of one winding 
of 145 ohms, and the non-inductive resistance, and on the other side of the 
other 145 ohm winding and the line, the latter being considered equal to 
the 350 ohm winding. This arrangement is to eliminate side-tone. 



Fig. 503o. 

Sometimes a different coil is used, as shown in Fig. 503r. This coil 
has a 7 /ig core and winding space about 3Vs, a primary of 1,000 turns, 10 
ohms, and two secondaries of 2,000 turns each, the first one measuring 
about 60 and the second about 240 ohms. The top secondary, or ter¬ 
tiary winding is connected to the monitor’s desk. 




COirWCTiOM 

OF PLUG FOR BREAST SET 


OF PLUG 



Fig. 503p. 


When either of these coils are used, an impedance coil of 165w 
resistance is placed in circuit as shown. 

The keys shown connecting to the trunk operators’ set, and to call 
wires, will be referred to later. 



Fig. 503q. 


Fig. 503r. 



While the ringing and listening keys are associated with the cord cir¬ 
cuits they will be referred to here. These are of various types, the usual 
form being shown in Fig. 503s. This is a very reliable key and seldom 
needs adjustment or repair. 

Where four party ringing is in use, the key shown in Fig. 503t, is 
used. The handle as shown is the listening key, the buttons, the ringing 
keys. 
















































COMMON BATTERY EQUIPMENT 407 

The cord circuit previously described will answer for connecting any 
two lines on the same board. When a trunked connection or one termi¬ 
nating in another office is to be handled, some other arrangement is neces¬ 
sary. 



Fig. 503s. Fig. 503t. 


Fig. 503u shows a trunk circuit used with the Western Electric No. 
1 switchboard. The originating, or outgoing end of the trunk consists of 
a jack, to the sleeve of which is connected a resistance equivalent to that 
of a cut-off relay. 



Assuming that an operator at this end of the trunk wants connection 
with some subscriber in the exchange wTiere the trunk terminates, she 
depresses an order wire key which puts her in connection with the trunk 
operator, who tells her what trunk to use. She then plugs into the trunk 
jack with the calling plug of the pair in use. 

Now tracing the current over the trunk, it will be noted that the only 
path available is through the 12,000 winding of relay A. The resistance 


















































408 


TELEPHONOLOGY 


of this is so high, that the supervisory relay in the calling operator’s cord 
is not operated, and the cord lamp continues to burn. Relay A, however, 
draws up its armature, thereby putting battery on the ring and guard 
lamp of the trunk, which is illuminated. The trunk operator now takes 
(if she has not already done so) the trunk plug, and applies the tip to the 
sleeve of the jack of the wanted line; if this line is busy she will get the 
busy test in the usual manner, because the tip of the plug is connected 
to her listening set, same as with the ordinary cord circuit when a key is 
thrown. This is explained in detail later, but it should be noted that the 
tip is only connected to the operator’s set through contact on relay B, and 
when this is energized the operators’ set is disconnected from the trunk, 
and tip of plug connected to trunk circuit instead. 

Assuming the wanted line to be idle the operator inserts the trunk 
plug. Battery now flows through the disconnect lamp, and through relay 
B which is operated, but the disc, lamp does not light because the 40 w 
shunt is placed around it by B, this shunt going to battery via armature 
of A. Relay B cuts off operator’s set. The operator now rings in the usual 
manner, and, when the subscriber answers, relay C, which is the super¬ 
visory relay, operates. This puts the 75 ohm winding of relay D in series 
with the 27 ohm winding of relay A and puts this total of only 100 ohms 
across the incoming trunk. This extinguishes the supervisory lamp in 
the cord o'* the operator at the calling office and, as relay D is drawn up, 
the ring and guard lamp is also extinguished. Now at the same time, the 
armature of D makes contact with its 35 iv winding, and battery imme¬ 
diately flows trough this path thus holding D locked after it is once pulled 
up by current through its 75 w winding, and making it independent of any 
future action of relay C. 

While the parties are talking, all lamps are out, but when the calling 
subscriber hangs up, and the calling operator removes the plug from the 
trunk jack, relay A immediately releases jts armature, which causes D to 
release; the disconnect lamp now lights, owing to the 40w shunt being 
opened at armature of A. Seeing the disconnect lamp light the operator 
takes down the plug. Now should the reverse condition of affairs hap¬ 
pen, and the trunk operator remove the trunk plug from the jack before 
the calling operator had finished with the trunk, the guard lamp would 
immediately light thereby notifying the trunk operator, because the arma¬ 
ture of A would supply the guard lamp with battery, and relay D would 
release as soon as the trunk plug was removed, thus completing the cir¬ 
cuit. This prevents mistakes, and enables the calling or “A” operator to 
handle the connection at all times. 

Fig. 503v shows the trunk operators’ set. The various parts have 
been described except the repeating coil, the terminals of which are mark¬ 
ed 1, 2, 4, 5. The wire marked X goes to the contact X Fig. 503w and is 
for the purpose of making the busy test. 

Suppose this wire X which normally connects to the tip of the trunk 
plugs, is touched on the sleeve of a busy jack, immediately battery flows 
from the jack to tip of plug, across contact X Fig. 503u to winding 4-5 
of repeating coil and to ground. This induces a current in winding 1-2 
which the operator hears as a click in her receiver, thus notifying her the 
line is busy. 

The incoming call wire goes to the order keys on the A operators’ 
positions of other offices. 


COMMON BATTERY EQUIPMENT 


409 


Bridged across this call wire is an ordinary battery restored drop, 
so that when the operator is absent from the board the calling operators 
can attract attention by ringing down this drop thereby lighting the call 
wire signal, as shown. A key is provided for restoring this drop. 

When the trunk circuit shown in Fig. 503u is used, it is necessary for 
the operator to keep on ringing the subscriber until he answers. A 
trunk with automatic ringing is shown in Fig. 503w. 



Fig. 503v. 


Upon the A or calling operator plugging into the trunk, a ground 
from the tip of her cord circuit is put on the t winding of relay A, operat¬ 
ing same. This draws up its armature, putting battery on relay D. Now 



if the trunk operator has put up the trunk plug (after making the busy 
test same as before) relay B is energized, and, when D operates supervi¬ 
sory lamp CL is extinguished. Relays B and D complete the trunk plug 
circuit through the tip side of repeating coil to erround, and the ring side 
to battery through supervisory relay C. In addition to this relay A also 
puts ground on the rinsing key common contact CC, which is closed when 
any button is depressed. Ringing current is supplied to the keys through 





















































































410 


TELEPHONOLOGY 


the windings of relay E which is of peculiar construction, and adapted to 
operate only through the low resistance path afforded the ringing current 
when a receiver is off the hook on the line being rung on. 

The ringing key is so constructed that when any button is depressed, 
common contact CC is closed and a circuit closed through the magnet coils 
MM, which hold the plungers locked. A key of this construction is shown 
in Fig. 503x. Instead of depressing the buttons when ringing, they are 
pulled sideways. 



Fig. 503x. 


Fig. 503y. 


Now suppose the operator has placed the trunk plug in a jack, relays 
A, B and D are operated, and she operates the ringing key, say the regular 
or alternating button. Immediately ± current flows from the interrupter 
INT, through relay E, out over the line, through bell and condenser and 
back again. This continues for 3 seconds, then battery is connected in 
place of the ringing current, for 2 seconds, and so on. Relay E is not 
operated, owing to the high resistance of the bell and condenser in the cir¬ 
cuit. It will be seen that this ringing will go on indefinitely without 
any action on the part of the operator after she once sets the key. When 
the subscriber answers it affords a low resistance path for the current 
and relay E immediately operates. This breaks the holding circuit 
through key magnets MM and the key is released and the circuit com¬ 
pleted through relay C. This draws up putting a ground on the ring side 
of the trunk through relay A, and extinguishing the supervisory lamp in 
the A operator’s cord, which remains out as long as C is closed, and lights 
again when C opens. Seeing this the A operator takes down her plug, this 
releases armature of relay A which releases D and, as this shunt is 
removed lamp CL lights, and the trunk operator takes down the connec¬ 
tion. 


The battery is connected in circuit with the ringing relay during the 
silent period, so that in case the subscriber should answer during that 
interval, the relay would be operated, and thereby avoid any delay and the 
subscriber getting a ring in the ear. The automatic alternate connection 
of the ringing and battery currents to the keys is accomplished by drums 
or commutators on the ringing machine as shown in Fig. 503y. The seg¬ 
ments are of varying lengths, thereby permitting the currents to remain 
connected for long and short periods as desired, with proper intervals 
between. 






COMMON BATTERY EQUIPMENT 


411 


With all the preceding trunk circuits, the trunk operator rings the 
wanted subscriber, therefore she controls the connection to this extent. It 
is desirable that the operator at the outgoing or originating end of the 
trunk, be able to ring the wanted subscriber, thereby having entire con¬ 
trol over the connection. This is especially desirable in long distance 
work, where the long distance operator has a message for some sub¬ 
scriber in a local exchange, the terminus of the trunk. 



Fig. 503z shows a trunk circuit in which the A operator can ring 
the B subscriber at will. This is known as the Long Distance toll trunk, 
and is commonly used between long distance office, and the district ex¬ 
changes in large cities. 

Referring to the figure, when the long distance operator plugs into the 
trunk, relay A is operated, and closes its contact putting a shunt around 
the disconnect lamp L. The trunk operator tests with the trunk plug in 
the usual manner, and plugs into subscriber’s jack with the trunk plug. 
This operates relay B, which completes the circuit from tip of plug to 
trunk circuit wiring, the tip being normally opened at relay B. Now the 
usual circuit can be traced from the battery and ground, through lepeat- 
ing coil and relay C to the plug. The ringing key is now operated by the 
trunk operator and is held locked by the magnetic clutch. This puts ring¬ 
ing current on the inside contacts of relay D, which however, is not opei- 
ated therefore the ringing current does not pass to the plug. The long 
distance operator now calls the subscriber by ringing on the trunk, this 
current operating relay E, which is responsive to ringing currents only, 
and is not operated by battery current, owing to the condenser in series 
with same. This relay is of peculiar construction, having a very heavy 
armature so arranged that it is slow acting and does not open its contac 
owing to the rapid impulses of the ringing current, but remains closed 
after once operating, as long as ringing current is passing thiough 1 . 
This relay is shown in Fig. 504. 

When E closes its contact, battery flows through D, which operates, 
bringing the tip and sleeve of the trunk plug circuit in contact with the 
ringing current and ringing the subscriber. Everything is cut off but the 
plug when relay D operates. 

















































































































































412 


TELEPHONOLOGY 


To keep the disconnect lamp from lighting during this operation, 
when E closes, an additional circuit is established to ground through F, 
which puts a local ground on A holding it closed and thereby keeping 
lamp L from lighting. 



Fig. 504. 


It will be seen that the long distance operator can call the subscriber 
at will, and that the ringing is entirely under her supervision. When the 
subscriber answers, relay C operates and puts battery on F, which closes 
and operates A, thus keeping ’amp L out during the conversation. This 
closing of relay C also puts battery on D in such a manner that it cannot 
be energized, thereby preventing it closing and ringing in the ear of the 
subscriber in case the long distance operator should ring, after subscriber 
answers. 



Fig. 504a. 


When the call is completed and the long distance operator removes 
her plug, relay A is released and opens, removing the shunt from the lamp 
L, which lights. The operator thereupon removes the trunk plug, which 
extinguishes the lamp and also releases the clutch on ringing key. 

The adjustment of the various relays used in these trunk equipments, 
is comparatively a simple matter and is the only attention the circuits 
need in the way of special maintenance. Various forms of relays, as fur¬ 
nished by the Western Electric Co., for this work, are shown in Fig. 504a. 
The supervisory relay C Fig. 503z is adjusted by means of a test similar 
to the regular common battery cords, this being described in connection 
with Fig. 503k. It is necessary to have a plug in the long distance jack 
end of the trunk when making these tests, so that the entire operation of 
the trunk may be observed, it being customary to plug the trunk into a 
jack connected to an ordinary subscribers’ set, and then simply “flash” 
the hook to test the relays. 










COMMON BATTERY EQUIPMENT 413 

^ run ^ s W ^h automatic ringing are used, such as shown in 
r 1 g. 503w, some means for testing the relay through which the ringing 
current passes (E in the figure) must be provided. This relay is designed 
to be operated by ringing or battery current when the line circuit is closed 
by the removal of the subscriber’s receiver from the hook. This relay 
not be operated when the circuit is closed by the l,000w> bell, and 
^ n j ' con oenser in series, which is the case when the subscriber is being 
called and the receiver is on the hook. In other words the combined imped¬ 
ance and resistance of the latter circuit is too great to allow sufficient cur¬ 
rent to flow to operate the relay. 

One winding of the relay is in series with the ± current going to the 
direct key. When the receiver is taken off the current divides, part 
flowing through the bell, and part through the transmitter and coil, this 
latter circuit is of sufficiently low resistance to permit sufficient current to 
pass to operate the relay, the current returning over the tip line, to ground 
at ringing key. 



The other winding of the relay is in series with the common or 
ground lead going to the 4 party keys. When a 4 party phone of the 
standard biased type, equipped with relay, as shown in Fig. 246 page 183 
is called, the pulsating current is connected to the line through the 100 m; 
resistance lamp and flows out over the line, returning through the four 
relays and condensers bridged thereon. These relays operate, connecting 
the four ringers to the lines, two between each side and the ground. 
We have seen that the ringing current is not continuous, but passes 
through an interrupter on the ringing current for two seconds, and battery 
for five seconds. The battery will pass through one of the windings of the 
relay, depending whether a “direct” or party line key is operated. As the 
battery current will not pass through a condenser, no current will flow 
through the relay during the time it is in circuit with the battery, unless 
a receiver is removed. 

The relay must be adjusted to work under two conditions, first with 
two 1,000 ohm bells and condensers bridged across a metallic line, and 
secondly, with four 2,500 ohm relays with condensers in series, the 
relays adapted to close a circuit through ringers to ground. 

A test set for accomplishing a satisfactory adjustment of the relay 
under these cor ditions, is shown in Fig. 504b. It consists of a 10,000 ohm 
volt-meter, in parallel with a resistance sufficient to make the combination 
measure about 3700 w. 

A second resistance is provided and connected with a key as shown, 
and when in circuit the entire combination measures about 750 w. 


























414 


TELEPHONOLOGY 


To use the set, the plug connected therewith is placed in any multiple 
jack, so that a ground is placed on the sleeve of the jack in the test set. 
The trunk plug is now placed in jack on test box. A plug is now placed in 
the outgoing end of the trunk and relays A, B and D, (Fig. 503w) being 
operated, upon depressing any ringing key, the ringing current will be 
connected to the trunk plug, and flow through volt-meter and resistance 
in test box. The relay is now adjusted so it will not operate unless the 
key in test box is pressed, thereby putting the 750 ohms across the circuit. 
When this is done, the relay should operate when either the “direct” or 
any party line key is used. 

When adjusting these relays care must be taken to see that the 
battery voltage is about normal, 22 volts. 

This test set affords an excellent method of testing the ringing cur¬ 
rent and connections to the keys for reversals. A double scale volt-meter 
should be used, so that it will not be necessary to reverse same. By noting 
the correct voltages and direction of deflection for each party line key, 
a reversal is quickly located. 

Those familiar with long distance work, realize the contusion caused 
by a subscriber calling for a long distance connection, and then, while the 
long distance operator is getting the connection, which sometimes requires 
20 or 30 minutes, some one calls for the party making the call and the line 
becomes busy, just as the long distance operator is ready to notify the 
party wanting the call, and has the toll line waiting. To prevent any 
delay, and hold the line of the party asking for the call, so that no opera¬ 
tor will put up a local connection on this line until the L. D. operator has 
finished, the “tone test” circuit has been devised. 



Figure 505 shows the circuit. Each operator is provided with one or 
more tone test plugs, located upon her table. A subscriber asking for a 
long distance call, is connected to the long distance operator in the usual 
manner. After his wants have been ascertained, the long distance opera¬ 
tor notifies the local operator to hold the line for long distance, and to 
accomplish this the local operator inserts the tone test plug in the answer¬ 
ing jack of the line. 

Immediately current flows through secondary of repeating coil S, 
through resistance R, through winding a of relay A, through relay B to 
sleeve of plug, energizing the cut off relay connected to the line in the 
usual manner and cutting off the line relay and lamp connected to that 
line. Relay B is also energized, and draws up its armature, putting a 







































COMMON BATTERY EQUIPMENT 415 

ground on the reverse winding b of relay A which is therefore not ener¬ 
gized, the two windings opposing each other. 

Now if another operator somewhere at the switchboard should get 
a call for this line, when she tested to see if the line was busy, she would 
hear a peculiar hum or tone’ due to the interrupted current flowing in 
the primary of the transformer S which is in circuit with the sleeve of the 
line, through the sleeve circuit of the tone test plug. She would accord¬ 
ingly report the line ‘busy/ The “tone” is caused by interrupting the 
battery by means of a commutator on the power generator of the exchange. 

If for any reason the subscriber should wish to call before the tone 
test plug is removed, upon taking the receiver from the hook, battery 
would flow through the windings of the RET. coil and relay C, and the 
latter drawing up its armature, would light lamp A, whereupon the 
operator would answer in the usual manner. 

Now supposing the tone test plug to be in the line jack, and the long 
distance operator is ready to complete the connection. She orders the 
trunk plug placed in the jack. The trunk operator does this, disregarding 
the tone test, which serves as a check to notify her that she is putting the 
long distance trunk plug into a line being held for a long distance con¬ 
nection. As soon as the trunk plug is inserted in the multiple jack of 
the line, an additional circuit is established from the sleeve to battery, 
through the sleeve relays in the trunk plug. This immediately causes 
relay B to let go its armature, because B is shunted by the lower resistance 
of the trunk cord relays. This removes the ground from winding b of 
relay A, and as the opposing influence of the B winding is no longer pres¬ 
ent, relay A closes its contact and the disconnect lamp B is illuminated. 
Sufficient current will pass through the a winding to operate A without 
closing B. The operator, upon seeing lamp B'operate, knows the long 
distance operator has completed the connection, and removes the tone test 
plug. 

When a line is in trouble, for instance short-circuited, some means 
becomes necessary to keep the line lamp from burning steadily and annoy¬ 
ing the operator. This can be accomplished by plugging into the line, 
thereby operating the cut-off relay. This method is however not advisa¬ 
ble, as it would permanently disable the line until repairs were made. 

A circuit for plugging up a line, so as to keep the line lamp from 
burning, and yet have the circuit in such condition that should the trouble 
disappear, the subscriber could still signal the operator is shown in Fig. 
506. The plug is located upon the switchboard, usually upon the blank 
table of the first section. Suppose a line to be in trouble, the plug is 
inserted in a jack connected to that line and key K pressed. This ener¬ 
gizes relay A which closes its contact, putting battery through one wind¬ 
ing of the repeating coil, the lamp, and on sleeve of plug, energizing the 
cut-off relay and putting out the line lamp. Now should any operator 
receive a call for this line, and test same in the usual manner, they will 
hear the “out of order” tone, a hum similar to the “tone test” and caused 
by interrupted battery flowing through the windings of the repeating coil 
as shown, this causing a noise in the sleeve circuit. The operator accord¬ 
ingly does not connect to this line but reports same as “out of order to 
the subscriber wanting the connection. 


416 


TELEPHONOLOGY 


From a study of the circuit it will be seen that when relay A oper¬ 
ates, it puts battery through relay B, which gets its ground through the 
sleeve of the plug via. the key K] and the cut-off relay. Relay B closes 
its contacts, putting a ground on the tip side of the line, and battery on 
the ring side, through relay A. Now as long as the line is short-circuited, 
or grounded on the ring side, relay A will remain closed serving as a sig¬ 
nal to the wire chief that the line is out of order, but if the short circuit 



Fig. 506. 

or other trouble is cleared relay A releases its contact, and as this opens 
the lamp and sleeve circuit, the lamp is extinguished, and the cut-off relay 
released and the line restored to its normal condition and the line lamp 
ready to respond, should a call be made. Should the trouble re-occur, 
pushing the button K will again set relay A and the trouble lamp and cir¬ 
cuit again put in operation. 

The jack J is provided for the wire chief to test from. The usual 
procedure when using this circuit, is for the monitor at the board, as soon 
as a trouble occurs, to plug same up, and press key K. This lights lamp 
on wire chief’s desk and seeing the light, he plugs into the jack, and by 
pressing K t , thereby flashing the line lamp in front of the operator, ascer¬ 
tains the number of the line and proceeds to clear the trouble. 

From the foregoing, it will be seen that a line in trouble is automati¬ 
cally transferred to the wire chiefs desk, and that it is not necessary for 
him to go to the switchboard to test, or ascertain the line in trouble. 

On common battery systems when the receiver is left off the hook, 
a steady signal results, and some means should be provided in every 
exchange to call the subscriber’s attention, and cause him to replace the 
receiver. Ringing in the usual manner will not do this, as the low resist¬ 
ance path afforded the ringing current through the transmitter circuit 
prevents the bell from ringing. 

A simple device for producing a howl in the receiver to attract the 
subscriber’s attention, consists of an ordinary magneto induction coil 
arranged in connection with a relay and battery, as shown in Fig. 506a. 
The relay R is a supervisory relay same as used in the Bell cord circuits. 
Battery B is the 22 volt exchange battery. When the plug is inserted in 
a line jack, the sleeve resistance operates the cut-off relay in the usual 
manner, and connects the coil circuit to line. This causes relay R to close. 
Buzzer Z, being in series with the primary of the coil, rapidly 





































COMMON BATTERY EQUIPMENT 


417 


breaks the circuit from the dry cells D, causing a loud howl or hum in the 
secondary which is transmitted to the receiver, the diaphragm of which 
gives forth a loud howl, and attracts the subscriber’s attention. When 
the receiver is replaced, relay R releases and the howl is stopped. 

The buzzer consists of an ordinary battery buzzer or bell, and three 
or more dry cells may be used. A condenser can be bridged across the 
buzzer contacts to prevent sparking. 



Fig. 506a. 


Fig. 506b. 


This arrangement can be used in magneto exchanges by omitting the 
relay and battery in the secondary circuit, and connecting the secondary 
directly to the plug. When this is done, the plug must be removed from 
the jack, and line tested to see if receiver is hung up, as there is no way 
to make the buzzer stop working, when used on magneto system. 

This arrangement is not powerful enough in some cases, so it is cus¬ 
tomary to equip the ringing machine with a commutator having a great 
number of divisions, thereby producing the howl, and to connect this cir¬ 
cuit to the line. The current must not be too strong, or it will demag¬ 
netize the receiver. 

A machine for producing the “howl” “tone test” and “busy back” is 
shown in Fig. 506b. In operation it is similar to the motor driven 
devices, but is designed for very economical battery consumption, so it 
will run from storage or dry cells and therefore may be used where there 
is no power available. 

The machine is mounted in a wooden case with glass top, and may be 
mounted in any convenient place, usually on the side of the converter or 
pole changer cabinet. The figure shows an outfit for two signals; others 
are provided by supplying other movements. 

It is at once evident to the most casual observer that the only reason 
for the use of the foregoing circuits with their automatic ringing and dis¬ 
connect features, etc., is a saving in time. Therefore time is really what 
the telephone company sells, especially in long distance work. The tim¬ 
ing of messages and equipment necessary to do this accurately, forms a 
most important part of the exchange equipment. 

THE CALCULAGRAPH is a machine for computing and recording 
elapsed time. In other words, it substracts the time-of-day a telephone 
toll conversation commences from the time-of-day it is finished, and prints 
the difference—the actual time in minutes and quarter minutes consumed 
in the talk. Incidentally, it also records the time-of-day the toll circuit 
was prt up and the conversation commenced. 















418 


TELEPHONOLOGY 


On the records made by the Calculagraph, the charge for toll service 
is reckoned in accordance with the schedule in vogue. Such schedules are 
made up, sometimes on a mileage rate—air line between towns and cities; 
sometimes on the nearest railroad distance and sometimes the rates are 
arbitrarily fixed to meet competition, without reference to distance. 

Calculagraphs have been used in telephone exchanges in the United 
States for about twelve years, the first lot of machines having been install¬ 
ed in 1895. 

These machines are now (1909) quite generally used throughout the 
United States and Canada in all telephone exchanges where toll business 
is handled. They have also become part of the standard equipment of 
toll switchboards in governmental telephone exchanges in Europe, Asia 
Africa and Australia. 

The use of toll circuits is an important part of the stock in trade of a 
telephone company. It is that which the company sells to the public at so 
much per minute and as such, it represents money just as fully as does the 
stock carried by any merchant. The public should pay for all it takes. 

The Calculagraph tells exactly how much use of a toll line is charge¬ 
able to the public including “excess time” or time extending beyond the 
period of the initial or minimum charge. 

Prior to the introduction of the Calculagraph in telephone exchanges, 
great difficulty was experienced in accurately recording the time con¬ 
sumed in the use of toll lines. It was generally conceded to be physically 
impossible for a toll operator to observe the time-of-day visible on a clock 
dial and write it down with pencil when the use of a circuit was com¬ 
menced, to repeat this operation when the use of circuit was discontinued, 
then subtract the one record from the other and get an accurate result, at 
last, that this could not be done without neglecting some of the other 
duties of operating. 

Various expedients were resorted to: sand glasses, stop watches, time 
stamps and other devices were tried, but were discarded as impracticable. 
Messages were timed at both ends of a toll line and both outward and 
inward operators made out tickets, monitored the connection, duplicating 
at intervals the question, “Are you through?” etc. Talking circuits over 
expensive toll lines were held up and “pay business” delayed while send¬ 
ing and receiving operators compared and adjusted the differences in 
their records of elapsed time on the previous message. (There usually 
were differences.) It was known by telephone managers that with meth¬ 
ods and appliances then available, errors in timing messages were likely 
to be made by either or both operators, but it was assumed that the aver¬ 
age of the two records of time elapsed would be “approximately correct.” 
Outward and inward toll tickets were herefore carefully compiled, com¬ 
pared and audited at considerable expense of clerical labor. Telephone 
toll service was charged for according to distance covered, in even periods 
of five minutes each. A fraction in excess of the initial period being for 
as another full period, and any time beyond ten minutes being charged as 
fifteeen, and so on. Concessions and compromises in charges for toll 
services were frequent and unavoidable. 

After the installation of the Calculagraph in telephone exchanges 
for timing toll messages the following reforms became possible and were 
at once inaugurated by the principal toll line companies in the United 
States. The practice of timing messages at the receiving end of the line 


COMMON BATTERY EQUIPMENT 419 

was discontinued and no inward tickets were filled out. The inward oper- 
a or was therefore able to handle twice as much business as formerly and 
twHie as much as the then outward operator was given. The expense 
or printing, compiling, comparing and auditing inward tickets was saved. 
1 he outward operator, relieved of the mental and manual effort required 
to observe and write down the times of commencing and finishing and to 
subtract the one from the other, was made more efficient in the other 
duties of operating. Talking circuits over toll lines were no longer held 
up and were available for “pay business” at all times. The mechanical 
record of elapsed time made by the Calculagraph on the outward switch¬ 
board was relied upon by both users of service and the company’s officials 

to be absolutely accurate and no concessions in charges for service were 
necesssary. 



Fig. 507. 

Fig. 507. Calculagraph mounted on Toll Switchboard of Am. T. & T. Co., New 
York City. 


The system of charging for service, by full periods of five minutes 
each, was changed so that all “excess minutes” after the first period were 
charged pro-rata, or at a proportionate rate per minute. By many of the 
telephone companies the initial period of charge for toll service was 
reduced from five minutes to three minutes, and by several companies to 
two or one minute. 

These changes in method of charging for toll service had often been 
discussed but never were thought possible or practicable until the install¬ 
ation of the Calculagraph, which made the timing o ’ messages a matter 
of certainty instead of estimate. The Calculagraph insured payment for 
all “excess minutes” used. There was no longer any doubt as to whether 
or not excess time had been used and no occasion to “give the customer the 
benefit” of such doubt. The Calculagraph enormously increased the reve 












420 


TELEPHONOLOGY 


nue from toll serivce; in some cases such increase was sufficient to pay 
a dividend on the capital stock of the company. The Calculagraph direct¬ 
ly benefitted the public (the consumer of telephone toll service), by estab¬ 
lishing an equitable basis for charges and by a reduction in the length of 
the period for the initial charge. 

The best method of mounting the Calculagraph on a toll switchboard 
is to sink it in the keyshelf midway between two operators so that ihe 
ticket plate of the machine shall be substantially flush with top of shelf. 
So placed one machine may be used by both operators. 



Fig. 507a. 

Two styles of cases for Calculagraphs are provided for this purpose. 
In the one designated case “B” shown in Fig. 507b the weight of the 
machine is supported by four large screws, which pass down through 
the wood into iron pillars of the case below the keyshelf. 




Fig. 507b. 


Fig. 507c. 


Case “C” shown in Fig. 507c is provided with a flange which rests 
on top of the keyshelf and the machine is secured against rotation by wood 
screws through the flange. 




















COMMON BATTERY EQUIPMENT 421 

The former style of case is preferred by some because it presents a 
neater appearance when mounted and the latter is preferred by others 
because it is more easily fitted and can be mounted without the services 
ot a skilled wood-worker. 

In small exchanges where toll lines are sometimes made to terminate 
at the end section of a local switchboard, the Calculagraph may be mount¬ 
ed on an extension self supported by iron brackets at the end of switch¬ 
board. . In such exchanges the Calculagraph is also frequently mounted 
on an iron pedestal secured to the floor. Such pedestals are adjustable in 
<< a 1 ” a C ulagraphs for use on pedestals should be ordered in case 

A . They are secured to the pedestal by screws through the bottom of 
case. 

Model 6 Calculagraph is the type of machine best adapted for use in 
timing toll messages; other models of Calculagraphs are made for use in 
different industries. 



Fig. 507d. Fig. 507e. 


The record made by Model 6 is shown in Fig. 507d. It indicates that 
the toll circuit was connected at 9 :45 A. M., and that the line was in use 
6*4 minutes. 

To commence a Calculagraph record, place card in left end of slot, 
face down, with top of card against back of slot and slide it toward the 
right until it hits the guide post. Push right operating lever outward 
until the rear end of cam touches top of main plate; this prints the time- 
of-day. See Fig. 507e. 

Then, without releasing hold of the operating lever or changing 
position of card, pull lever inward until front end of cam touches main 
plate; this prints the two elapsed time dails. Remove card and commence 
other records on other cards in the same manner. See Fig. 507f. 

To close a record, at the end of a period of time under measurement, 
place the card containing the beginning of that record back into the slot 
in the same manner and in the same position as in Fig. 507f. and pull the 
left hand operating lever inward until its cam point touches the plate; 
this will print arrows in the centre of the two elapsed-time dials. The 
arrows will point to figures of the dials which represent the time which 
has elapsed, since that record was commenced. See Fig. 507g. 









422 


TELEPHONOLOGY 




The paper of which cards are made should be heavy enough to re¬ 
main flat while being shoved into the slot of the Calculagraph. The opera¬ 
tor will handle such cards more rapidly and insert them more accurately 
than if made of thin paper which will crumple when pushed into the slot. 



Fig. 507f. Fig. 507g. 

Any quality of paper on which a lead pencil will make legible marks 
will be suitable for cards, but paper having a glazed surface will not 
receive satisfactory impressions from the printing dials. 

Booklets containing more detailed information in regards to mount¬ 
ing, using and repairing the Calculagraph, are supplied by the manu¬ 
facturers and are usually packed and shipped with the machines. 



CHAPTER XII. 




HARMONIC PARTY LINE SYSTEMS. 


The name Harmonic Party Line System has been given to a system 
of selective bells for telephone party lines which has come into very gen¬ 
eral use in the last four years among the independent telephone companies 
of this country. Referring to Kempster B. Miller’s book, “American Tele¬ 
phone Practice,” you find the following passage which I consider the most 
lucid explanation of the principle involved in this class of systems which 
I have ever seen. He says: 

“These systems, with one exception, make use of the fact that every 
pendulum or every vibrating reed has a natural period of vibration, and 
that it can be made to take up this vibration by the action of a succession 
of impulses of force occurring in the same frequency as that in which the 
reed or pendulum vibrates. A familar example of this is found in one 
person pushing another in a swing. The swing has its natural period of 
vibration depending on the length of the ropes, and a gentle push applied 
at proper intervals by the person on the ground will cause the swing to 
vibrate with considerable amplitude. If the pushes are applied at inter¬ 
vals not corresponding to the natural period of vibration of the swing, 
many of them tend to retard rather than help its vibrations, so that a use¬ 
less bumping results, producing but little motion.” 

When a tuning fork is struck near a piano, which is in perfect tune, 
a corresponding note of the instrument will sound out clearly. You have 
already probably noticed that when you make a musical sound in a room 
either by whistling, singing, or playing a musical instrument, that some 
object, such as the globe o a chandelier or the strings of a piano, will pro¬ 
duce the oricrinal sound. In the foregoing illustration the sympathetic 
tone was produced by impulses of force transmitted through the medium 
of the air from the original sounding body to the one reproducing it. 
When the tuning fork was sounded, the resultant air vibrations came into 
contact with every string in the niano, but they were strong enough to 
move only the one which happened to be in tune with them. We can im¬ 
agine that the noise made by the firing of a revolver in the same room 
would cause all the notes of the piano to sound at once regardless of pitch. 
The pendulum of a clock or the balance wheel of a watch is kept in motion 
by the almost infinitesimal blows of their escapements, which blows are 
applied at exactly the proper instant, but we also know that both a clock 
and a watch run faster when first wound, when the spring is strong, than 
when nearly run down. For instance, in Mr. Miller’s illustration of the 
swing, it is evident that if the individual doing the pushing were suffic- 

( 423 ) 




424 


TELEPHONOLOGY 


iently strong he would be able to operate the swing regardless of whether 
the impulses of force employed occurred in the natural period of vibra¬ 
tion of the swing or not. I mention these exceptions to the laws of har¬ 
monic vibrations to bring to your notice the importance of the strength as 
well as the frequency of the impulses of force applied. We come now to 
the application of the foregoing principles to the commercial selective 
party line system. All that is necessary to accomplish this result is to dis¬ 
tribute your tuned devices, which in this case are the bell armatures, at 
the telephone subscribers’ stations, and operate them by electromagnets 
energized by alternating currents of electricity of the proper frequencies 
and strengths sent over the telephone lines. Selective systems of this kind 
both for telegraphy and telephony were early designed. 

Mr. Miller says: “This idea was used in telegraphy before the birth 
of telephony. A number of currents of different rates of vibration were 
impressed upon the circuit by as many different transmitters, each par¬ 
ticular rate of vibration being capable of operating a reed in one of the 
receiving instruments and producing no effect on the other. By this 
means each receiving instrument was capable of picking out only those 
signals sent by the transmitter having the same rate of vibration, and 
thus all of £he transmitters could be used simultaneously in the same cir¬ 
cuit, producing a system of multiplex telegraphy.” One of the earliest 
systems of this kind was that invented by Thomas A. Edison and patent¬ 
ed in 1877. 


■ -Vi i " 

Fig. 508. 











Fig. 508 represents a copy of the patent drawing. In Edison’s sys¬ 
tem a series of magnets, whose armatures were reeds tuned to respond 
to different frequencies, were connected in series in the line. At the side 
of the drawing is illustrated a mechanism for producing the pulsating 
currents of proper frequencies. In front of each armature, you will no¬ 
tice, is a small Helmholtz resonator to increase the volume of sound. It 
was possible by means of this combination for a number of messages to 
be sent over a line simultaneously. A great many harmonic telegraphs 
have been invented, prominent among the inventors are the well known 
scientists, Elisha Gray and Professor Rowland. 
















HARMONIC PARTY LINE SYSTEMS 


425 


The first harmonic selective party line system was that invented by 
J. B. Currier and patented by him in 1881, and used for several years by 
the New England Bell Telephone Company. Fig. 509 represents a copy 
of the patent drawing. In this system the electromagnets with their arm¬ 
atures, which in this case contained the bell tapper, were arranged In 
series in the line the same as in the Edison harmonic telegraph. Currier 
produced his pulsating currents by means of pendulums of different 
lengths, which pendulums were provided with contacts for interrupting 
the ringing current. 



The next improvement invented in this line was the system of J. A. 
Lighthipe’s, patented in 1895, which was used to a limited extent by the 
Bell Telephone Company on the Pacific coast, Fig. 510. Lighthipe’s sys¬ 
tem is almost identical with the harmonic selective party line systems in 
use today. He was the first one to introduce the condenser in series with 
the bell across the line to prevent the central office current from flowing 
through the magnet coils. 







































































426 


TELEPHONOLOGY 


operation of systems of this class, the current impressed on the ringing 
mechanism must be of constant frequency and of approximately uniform 
potential. When we look back on early telephonic conditions, we see that 
these things were not available. How could we expect to deliver a cur¬ 
rent of constant frequency and potential to our bells when we had bad 
lines, no storage batteries, no ringing machines, and if we had had this 
apparatus we would not have had the splendid sources of electric power 
at present available to operate them with. What has really made possible 
the use of harmonic party line systems has been the introduction in the 
last few years of modern engineering methods into the telephone business. 
With the advent of the educated telephone engineer came good lines and 
modern power apparatus, making possible the use of much more refined 
central office and sub-station apparatus. 

Early telephone experts never expected that the time would come 
when each telephone subscriber would be provided with an individual me¬ 
tallic circuit, consequently a large amount of work was done by them 
along the lines of developing selective party line systems. I myself re¬ 
member that in St. Louis, in the early eighties, a system which employed 
the “step by step” mechanism was used and as high as sixteen parties 
were rung selectively on one line; this was known as the “Bliss” system. 
All one has to do is to investigate the United States patent records to con¬ 
vince himselJ that there is nothing new in selective systems; every pos¬ 
sible combination of “step by step” mechanisms, polarized relays, and, in 
fact, every device known to the mechanician and electrician, were combin¬ 
ed to produce different kinds of party line systems. 




If a committee of telephone engineers were asked to decide the ques¬ 
tion as to what things were most desirable in a party line system, their re¬ 
port would be as follows: No earth connections, no relays, no adjustable 
springs or ewights, no step by step mechanisms, and that the ringing of 
the bells should not be appreciably affected by the capacity or resistance 
of the line. The only way that such a specification could be satisfied would 
be to have bells whose operation depends upon mechanical tuning. 

In order to bring out clearly the advantages of a system using clean 
metallic circuits as compared with those using earth connections, it will 
be necessary to describe briefly the latter. 

Referring to Fig. 511, we have represented a subscriber’s telephone 
line consisting of wires L, and L 2 . Connected to earth from the L, line 
are the bells R, and R,; connected to earth from the L 2 line are the bells 












































































































































HARMONIC PARTY LINE SYSTEMS 


427 


R a and R 4 ; bells R, and R :{ are responsive to pulsating currents of positive 
sign and bells R 2 and R 4 to pulsating currents of negative sign. Genera¬ 
tor Gj furnishes pulsating current o positive sign and generator G.. pul¬ 
sating current of negative sign. The switches, K„ K._„ K 3 and K 4 are 
provided at the central office for connecting current of the proper kind 
to line. 

When we consider a system such as that illustrated in Fig. 511 we 
find that the following objections are present: on account of the presence of 
earth connections at the sub-stations, the lines are susceptible to bad in¬ 
ductive disturbances, due to electric railway, alternating power and 
lighting circuits and telegraph. It is apparent that in order that subscrib¬ 
ers be rung selectively that each bell be connected to the proper side of 
line. In other words, the operator when she wishes to ring stations 1 and 
2, projects either positive or negative pulsating current on to the h 1 half 
of the metallic circuit, and when she wishes to call stations 3 and 4, she 
connects plus or minus current to the L, side of the line. 

Now, if a line be transposed, say at T, to prevent inductive troubles, 
or if the wire chief at the central office happens to get a jumper reversed in 
the process of making a cross connection on the distributing frames, the 
currents sent out would go to the wrong side of the line, and a wrong sub¬ 
scriber be called, thus causing endless trouble. This class of faults is con¬ 
stantly occurring to my knowledge. In installing telephones in a system 
such as Fig. 511, the installer is always obliged to locate accurately the 
proper side of the line before connecting it to the telephone, which opera¬ 
tion entails expense and chances for mistakes. When an operator in this 
system rings a subscriber, say No. 4, with the minus pulsating current, 
and during the process of ringing the subsciber removes his receiver from 
the telephone hook, part of the current is carried over to the other half 
of the line and the bell connected to it which responds to like current, (No. 
2) will consequently give a false ring. 

Now we come to the description of a modern harmonic selective sys¬ 
tem. Referring to Fig. 512, L, and L„ represents the two sides of a metal¬ 
lic circuit telephone line. R,, R,, R 3 and R, are mechanically tuned tele¬ 
phone bells, each having connected in series with it a one microfarad con¬ 
denser across the line. G\ G-, G 3 and G 4 are generators designed to ring 
them. K,, K.„ K : , and K 4 are switches used by the operator for connecting 
the currents of proper frequency to line. It is evident that no transposi¬ 
tion of the line at any point or of the terminals of the instruments can 
affect the operation of this kind of a system, and inasmuch as each bell 
responds to an entirely different current, no “cross rings” can be pro¬ 
duced by the removal of the receiver during the process of ringing. It is 
also evident that when telephones are being installed, they can be connect¬ 
ed to the line without care or reference to polarity, in the same manner 
that incandescent lamps are connected to a lighting circuit. 

Two of the first problems that present themselves in designing a har¬ 
monic party line system are the selection of currents of proper fre¬ 
quencies and voltages and the method of producing the same. Elisha 
Gray found during his experiments with harmonic telegraph, that fre¬ 
quencies which were related in a ratio of 1, 3, 5, 7 and 9 produced the 
least interference. It is evident that to produce currents whose fre¬ 
quencies are related in the above manner, it would be necessary, if one 
driving motor were used, to use belted or geared transmission which is 
not desirable. It was found that currents whose frequencies were related 


428 


TELEPHONOLOGY 


in a ratio of 1, 2, 3 and 4 were sufficiently non-interfering for commercial 
purposes. Currents or frequencies of 2,000, 4,000, 6,000 and 8,000 were 
finally adopted and were generated by a set which consisted of a motor 
direct connected to 2, 4, 6 and 8 pole generators, the whole outfit running 
at a speeed of 1,000 revolutions per minute. A set of this kind is illus¬ 
trated in Fig. 513. It was found by experiment that high frequency bells 
required more power to operate them than the low frequency ones, and 
consequently it was found necessary to step up the voltages of the genera¬ 
tors as the frequency increased. The voltages which were finally found 
to be the best were for 16 2-3 cycles, 60 volts; for 33 1-3 cycles, 100 volts; 
for 50 cycles, 135 volts; and for 66 2-3 cycles, 180 volts. These harmonic 
ringing sets are provided with a governor, by means of which the speed 
of the motor is kept constant regardless of the vibrations of voltage in the 
power circuit. 



Fig. 513. 

We now come to the design of the harmonic bell itself. The follow¬ 
ing points are essential to a successful harmonic ringer: Its armature 
must be in perfect tune with the current designed to operate it; it must 
remain in tune, after once leaving the factory, indefinitely; it must be in¬ 
terchangeable with the ordinary single party telephone ringer, for the 
reason that a great many of the operating companies find it necessary to 
change over their old to the new system; it is desirable that the general 
appearance of the ringer after being installed be the same as that of the 
ordinary single party ringer, it being sometimes desirable that the tele¬ 
phone users be in ignorance of whether other subscribers are using party 
or single line service. 

Figs. 514 and 515 represent a modern harmonic party line ringer. 
The design of this ringer is very similar to the ordinary telephone ringer 
with the exception that all of its parts are more massive. The principal 
difference lies in the fact that its armature is mounted upon a spring in¬ 
stead of being pivoted. The construction and mounting of the armature 
is shown in Fig. 514. Each complete armature consists of two punchings 
P' and P 2 , a flat steel spring S, a steel tapper rod T, a weight W, and the 
mounting block B. In riveting together the punchings P l and P 2 , the low¬ 
er end of the mounting spring S and the upper end of the tapper rod T 




HARMONIC PARTY LINE SYSTEMS 


429 


are firmly attached to the armature as a whole. The part of the tapper 
rod which is fastened between the punchings is knurled so that it will not 
slip. The upper part of the mounting spring S is clamped between the 
block B and plate D which are fastened together by means of two heavy 
iron rivets. All the riveting in connection with the armature is done in a 
power press in order that the highest possible rigidity be obtained for the 
completed article. The block B is provided at its two ends with threaded 



Fig. 514. 


trunions C, designed to fit into the slots X of the ringer yoke. After the 
block B has been slipped into place it is held by the clamping- of two heavy 
nuts provided on its trunions. It was found necessary to make the tapper 
rod T very much more rigid than that used in the ordinary ringer for the 
reason that if it was not so, false vibrations would be set up in the tapper 


s 


Fig. 515. 

rod between the weight W and the armature. In the manufacture of the 
spring S, special spring steel is purchased in the shape of long ribbons 
of the proper thickness and width, similar to heavy clock spring, and then 
cut up and perforated in an ordinary punch press. It was found necessary 
as shown in the accompanying illustrations, to provide these ringers 
with a very massive micrometer adjustment for the gongs, otherwise the 















430 


TELEPHONOLOGY 


heavy tapper weights would batter back the gongs out of adjustment dur¬ 
ing the process of ringing. 

The method of tuning these ringers is as follows: A set of standard 
adjusting weights exactly similar to those shown in Fig. 515 with the ex¬ 
ception that they are provided with small set screws to clamp them to the 
tapper rod, are used. The bell to be tuned, minus the gongs, is clamped 
in a very rigid frame and a very weak current of proper frequency is ap¬ 
plied to its electromagnet. On account of the current being extremely 
weak, the armature will not operate unless it be in absolute tune with it. 
The tuner raises and lowers the tuning weight until a position is reached 
in which the armature vibrates violently; when the weight is in this posi¬ 
tion he knows that the armature is in tune. He then scratches the tapper 
rod at the upper end of the weight with a small file, and removing the 
testing weight, he pushes on an exactly similar one by means of a small 
press provided for the purpose. It can be seen by this construction there 
are absolutely no adjustments to be tampered with by unskilled labor. A 
steel wrench is furnished for the different nuts of the ringer, so that there 
is no excuse for the telephone repairmen using their pliers on them. The 
assembled armature is now slipped into place, clamped in the proper posi¬ 
tion by means of the nuts C, Fig. 514. A proper air gap between the mag¬ 



net pole piece and the armature is obtained by raising and lowering the 
yoke which supports the armature. This is done by means of adjusting 
nuts threaded over the magnet cores as shown in the accompanying illus¬ 
trations. The gongs are not placed in position on their posts until the bell 
is mounted in the telephone box. In fact the bell will operate as a buzzer 
without the gongs, thereby showing that its proper work is not dependent 
upon the presence or absence of the same. The armature and tapper rod 
normally stand in the central position with reference to the pole pieces 
of the magnets and gongs (Fig. 516). On account of the normal position 
of the armature, with maximum air gaps, giving a minimum magnetic 
pull, it will not be affected unless the energizing currents are in exact tune 
with it. When-the proper current is thrown on to the line, the ball will 
then be thrown into violent vibrations, andtheends of the armature brought 
into contact with the pole pieces, which are bare. The armature in this 
position is very strongly attracted and comes to a sudden stop on the pole 
pieces. The gongs are so adjusted that the tapper ball will have to spring 
about one-thirty-second of an inch in order to hit them. When the arma¬ 
ture is alternately coming into contact with the two pole pieces of the per¬ 
manent magnets, the magnetic pull is so great that it is impossible for the 
striking of the gongs to throw it out of tune. The ringing position of the 
bell is shown in Fig. 517. 





































HARMONIC PARTY LINE SYSTEMS 


431 


It is a well known fact that a device in tune with the energizing force 
is many times more efficient than one which is not. In working with these 
absolutely tuned bells I have found that they can be constructed to give 
any degree of sensitiveness. 



Fig. 517a. Dean Electric Co. Harmonic Ringer. 

While the motor generator ringing machines previously described 
serve their purpose, they necessarily limit the use o" the harmonic system 
of ringing to such exchanges as can obtain the necessary electric current 



Fig. 518. Dean Electric Co. Harmonic Converter. 

for their operation. These machines are furthermore expensive in fi r st 
cosC also in operation and maintenance, when compared to the cost of a 
telephone switchboard and the cost of current required to operate it. 










432 


TELEPHONOLOGY 


Thus many small exchanges have been prevented from installing the har¬ 
monic system, and a big demand created for a simple and inexpensive 
method of producing the harmonic currents without the necessity of 
special power circuits and without a big current consumption. The har¬ 
monic converter shown in Fig. 518 is a result of this demand. It is made 
up of four separate units each consisting of a pole changing vibrator, a 
transformer adapted to the frequency of its associated vibrator and de¬ 
signed to give the proper voltage in its secondary winding for the opera¬ 
tion of the harmonic ringers previously described, and a condenser also 
suitably proportioned to the electrical conditions of the circuits. These 
units are shown with their connecting wiring in Fig. 519. It will be seen 
that the vibrators, V lt V 2 , V 3 and V 4 have electromagnets operating 
armatures similar to the action of an ordinary electric house bell. Upon 



Fig. 519. 

these armatures are mounted two springs, which are connected 
to the terminals of a source of direct current supply. Four contacts are 
arranged, two on either side of the springs, so that when the armature is 
drawn up the current will be allowed to flow through the primary wind¬ 
ing of the transformer, and when the armature swings back, these 
latter contacts are cleared and the other two contacts are made, causing 
current to flow in opposite direction through the same primary winding. 















































































































HARMONIC PARTY LINE SYSTEMS 


433 



The condenser C, which is placed across the primary winding of the trans¬ 
former, takes up the discharges from the coil and prevents sparking at 
the vibrator contacts. It also assists in rendering the alternating effect 
in the primary winding more uniform and efficient. One of the secondary 
terminals on each of the transformers is connected to a common conduc¬ 
tor, and together with conductors from the other four free terminals, 
serve to carry the four frequency ringing currents to the switchboard. 

Unlike the direct connected motor driven multi-frequency generator, 
the separate units of the harmonic converter allow the use of the most de¬ 
sirable frequencies for non-interference in ringing. Thus in some har¬ 
monic converters, eight different frequencies are generated, each tuned so 
as to operate its proper bell without causing any of the remaining seven 
bells bridged across the same line to ring. This eight party selective sys¬ 
tem, without the use of grounds or third-wire connection, is only one pos¬ 
sibility of the harmonic converter, and represents what can be done in 
practice if the demand should arise. An incidental advantage in the use 
of separate units for each frequency is that each vibrator will continue to 
operate perfectly even though one or more of the other converters or as¬ 
sociated apparatus is disabled. In every case the regular subscribers can 
be rung, as any of the frequencies can be used for this purpose; also all 
party line subscribers can be rung excepting those affected by the dis¬ 
abled frequency. Thus the use of a duplicate set of harmonic converters 
is not imperative, although desirable, as the repairing of a defective part 
can be easily made. 


Fig. 520. 

The vibrator or pole changing mechanism of the harmonic converter, 
shown in detail in Fig. 520, is made with massive parts rigidly put to- 

28 







TELEPHONOLOGY 


% 434 

gether so that the continual vibration of the armature will not work them 
loose. The armature itself is made from one piece of tempered steel cut 
away at its upper part so as to form a thin spring portion as shown 
in Fig. 519. This construction obviates the use of rivets, and gives a solid 
portion of the metal at its top which can be rigidly held in the vibrator 
frame. The reduced portion of the armature is made rather long so as to 
give a free and easy armature movement and an indefinite li e to the 
spring. At the lower end of the armature is attached an adjusting weight 
which is used to get the final tuning of the mechanism to the proper fre¬ 
quency. These weights can be raised and lowered during the process of 
tuning, and securely clamped in place at the proper position. The main 
difference in the rate of vibration of the armature is obtained, however, 
by making its reduced or spring portion of different thicknesses, the high¬ 
est frequency having the thicker spring. Vibrators constructed on these 
lines do not very perceptibly form a uniform rate of vibration, even with 
great changes in the voltage of the operating circuit. The only noticeable 
effect is the variation in the amplitude of movement, but this has not been 
found a serious obstacle when operating within the limits of the voltages 
usually met with in practice, a change of thirty to forty per cent in the 
case of storage batteries. A governing mechanism is therefore unneces¬ 
sary, as the proper frequency is always maintained. 



Fig. 521. 


The transformers used in the harmonic converter are built after the 
pattern of those used in electric lighting, with a very efficiently closed 
magnetic circuit. The amount of iron as well as the design of the windings 
are varied to suit the frequency and voltage required at the secondary ter¬ 
minals, the lowest frequency having the greatest amount of iron and the 
smallest voltage. The transformers shown in Fig. 521 are of fifty-five 
watts capacity each, excepting that of the low frequency which is made 
for twenty-five watts, as not so much power is used in ringing the low fre¬ 
quency bells. The most efficient design of these transformers was found 
by experiment rather than by following the regular formulas used in 
transformer design. When made according to the latter, the exciting or 
no load current is excessive, due to the character of the alternating cur¬ 
rent produced by the pole changers. As subsequently shown, the trans¬ 
formers finally adopted are very economical in current consumption, and 
will stand a very heavy overload. 

The first experiments on the harmonic converter were directed to- 











HARMONIC PARTY LINE SYSTEMS 435 

wards reducing the number of contact points in the vibrators, and the 
most promising scheme developed was the use of a double primary trans- 
former with a vibrator having two contacts, arranged one on either side 
ot the armature, and so connected as to cause current to flow, first in one 
primary coil of the transformer and then in the other coil but in opposite 
direction. Thus an alternating current was produced in the secondary 
winding. Condensers were placed across each of the primary windings of 
the transformers to reduce sparking at the contacts and assist in the cir¬ 
cuit action. It was found, however, that the use of two primaries greatly 
reduces the efficiency of the transformers, giving less out-put and a great¬ 
er no-load or exciting current than when one primary is used. Also the 
breaking of the current at one vibrator contact, which necessarily has a 
comparatively small amount of movement, limits the output of the ma¬ 
chine as well as restricts its use to low voltage primary circuits. 

A multiple break and a complete reversal of the current in the vibra¬ 
tor, as shown in the perfected harmonic converter, were thus found neces¬ 
sary to. correct these evils. The breaking of the current at the two con¬ 
tact points simultaneously not only reduces the voltage at each break to 
one-half that of the primary source, but doubles the distance of contact 
opening in the circuit, thereby allowing the harmonic converter to be 
operated from the higher voltage primary power circuits. 

It has been found in practice that the various frequencies used in the 
harmonic system of party line ringing, when produced by properly de¬ 
signed alternating current generators, give no noise in the talking circuits 
or inductive disturbances in the lines when ringing. This is probably due 
to the character of the alternating current which has a curve approaching 
that of a true sine wave. The use of a transformer and condenser in a 
harmonic converter tends to smooth out the current curves produced by 
the pole changing vibrators so that the quiet effect of the sine waves is 
obtained. 

Another and more important problem presented itself when operat¬ 
ing the harmonic converter from a storage battery of a common battery 
exchange, as the rapidly recurring changes in potential, due to the action 
of the vibrators, is sufficiently strong to make the entire talking system 
noisy. When the exchange battery is of large size and the taps for the har¬ 
monic converter are taken directly off its bus bars, this noise is only slight¬ 
ly perceptible. But any disturbances of this nature are not to be tolerated 
in a modern exchange installation, so that efficient means had to be pro¬ 
duced to entirely overcome this defect. The use of a retardation coil of 
sufficient impedance to kill the noise in the talking circuits cuts down the 
efficiency of the harmonic converter to such an extent that its output is 
not great enough to ring the bells of the party line system. However, a 
device was produced as shown in the diagram, Fig. 519, which allows the 
use of a very high impedance coil and still retains the full efficiency of the 
harmonic converter. This retardation coil is placed in the supply or feed 
wire between the main exchange battery B, and the harmonic converter, 
and between them is bridged or floated an auxiliary batt°ry B„. Like 
poles o c this battery and the main exchange battery are connected to the 
same wires, so that the auxiliary battery is kept constantly charged, and 
in fact, is called upon for no discharge except when the electromotive force, 
due to the main battery is choked down and prevented from providing a 
peak current, the deficiency beine - then momentarily supplied for each 
wave by the auxiliary battery. In fact, the auxiliary battery may be call- 


436 


TELEPHONOLOGY 


ed an equalizer, since it really takes up and absorbs the noisy back surg- 
ings, which would otherwise produce a disturbance in the entire common 
battery system. This auxiliary source of current supply can be a small 
storage battery, or even electrolytic cells, but in practice ordinary dry 
cells have served the purpose. 

The power consumption and actual results obtained in practice from 
harmonic converters with fifty-five watt transformers will serve as an ex¬ 
ample of the possibilities of this piece of apparatus. With a twenty-two 
volt source of current, it requires less than 0.58 of a watt to operate the 
four vibrators, while with the primaries of the transformers connected, 
this consumption is increased to about 6^ watts. The latter figure repre¬ 
sents the total no-load power required when the harmonic converter is 
connected for regular exchange work. This machine will furnish power 
to ring simultaneously over fifty fully loaded lines of four bells each, and 
while an excessive load, it yet remains in the safe limits of operating. 
Such a machine will do easily all the ringing of an exchange of 6,000 
lines. 

When no direct current source of power is available, primary bat¬ 
teries can be successfully used for operating the harmonic converter. In 
the case of small exchanges, dry cells are used to a large extent. In any 
event it is desirable to have the primaries of the four transformers nor¬ 
mally disconnected from the vibrators so that the no-load current will be 
at a minimum. This is done by means of a magnetically operated switch 
or relay, which is in turn operated by contacts on the ringing keys. As 
previously stated, the total no-load power consumed is less than 0.58 of a 
watt—the energy required for keeping the vibrators in motion. 

The foregoing description of the development of the Harmonic prin¬ 
ciple, and its application to telephone work, was written by William W. 
Dean, and is reproduced here by permission of “Telephony.” 

The Dean Electric Co., have been notably active in the development 
and perfection of this system, especially the perfection of the vibrating 
converter. The following instructons for the care of converters applies 
particularly to the Dean machine, although the general instructions for 
tests and the location of troubles, etc., can be applied to the several other 
makes of machines now on the market. 

The Harmonic Converter (registered Trade-Mark) is designed to pro¬ 
duce four alternating currents of different frequencies from one direct 
current source in a manner similar to that employed in an ordinary single 
type pole changer. A direct current of low voltage (our standard Con¬ 
verter is designed for 22 volts) is first changed to an alternating current 
by a pole changing mechanism and then stepped up in pressure by a trans¬ 
former so as to give a voltage sufficient to ring regular or party line ring¬ 
ers on all kinds of telephone circuits. Condensers are placed across the 
primary windings of the transformers so as to prevent sparking at the 
pole changing contacts, and also to assist in the action of the transformers. 

The complete Harmonic Converter, as covered by these instructions, 
includes four sets of elements just describet; i. e., a pole changing vibra¬ 
tor, a transformer and a condenser for the latter. In some cases each set 
also contains a condenser in series with a non-inductive resistance, the 
whole being placed across the motor contact of the vibrator to prevent 
sparking as subsequently described under the heading “To Prevent Spark 
at Motor Contact.” 


HARMONIC PARTY LINE SYSTEMS 


437 


The Harmonic Converter is designed to operate with an extremely 
small current consumption, about 1-40 of that required by the machines 
available before its advent, and its design is such as to require very little 
attention. Like all other electrical apparatus, the Harmonic Converter is 
susceptible to troubles if neglected, although it may continue to operate, 
even when abused, but with inefficient results. However, inefficient ope¬ 
ration, in time, will produce permanent defects which ares ure to disable 
the machine. Therefore, we have compiled the following instructions 
taken from personal observations and from valuable suggestions received 
from several of the users of the Harmonic Converter. 



Fig. 522. End view Dean Ringer. 


The instruction card found inside of the door of the Converter cabi¬ 
net gives detailed information regarding that particular machine. The 
material herein contained is of a supplementary and general character. 

Following are some brief answers to questions regarding the Har¬ 
monic Converter which will assist in its proper installation and care: 

What source of current is required for operating the Harmonic Con¬ 
verter ? 

A direct current such as can be obtained ^rom a storage battery or 
primary battery. If the proper wiring is used and the service not too 
heavy, dry cells can be employed. We make a special Harmonic Conver¬ 
ter for the latter purpose. 

What is the proper voltage of battery current for operating the Har¬ 
monic Converter? 

It should be kept at about 22 volts, never lower than 20 or over 24, if 
the best results are desired. See the instruction card attached to Har¬ 
monic Converter for the extreme limits. 

If storage batteries are used for operating the Harmonic Convei tei, 
how many cells? 

Eleven cells connected in series. Under normal conditions this bat¬ 
tery will give 22 volts or about two volts per cell. When the cells are be- 






438 


TELEPHONOLOGY 


ing charged, the voltage will increase to over 21/2 volts per cell, giving a 
maximum of about 28 1/2 volts for the eleven cells. This is too high for 
good results and we recommend that a tap be taken off the 9th cell so that 
the Harmonic Converter can be operated at its normal voltage during the 
charging period. See “Battery Reversing Circuits” for wiring of an end 
cell switch. 

If dry cells are used for operating the Harmonic Converter, how 
many ? 

When the cells are fresh sixteen in series will be sufficient as each 
cell gives about iy<± volts making a total of 24 volts. If No. 6 dry cells 
are used, it will require four sets of these series arrangements connected 
in multiple or a total of sixty-four cells. 

The voltage of a dry cell will gradually fall below 1.5 after being in 
use for a short time so that more cells must be added to each series in 
order to keep the operating current at its normal or 22 volts. Always add 
the same number of cells to each series but never more than two, making 
a total of 18 for each series, or seventy-two in all. See ‘“Battery Revers¬ 
ing Circuits” for wiring of a Dry Cell Harmonic Converter. 

How long will dry cells last if used to operate the Harmonic Con¬ 
verter? 

This depends entirely on the amount of ringing done and the method 
of operating the Harmonic Converter. If a starting relay is used and the 
vibrators are operated only when ringing, a set of cells should last at least 
six months on a small exchange (two operators’ positions). The life of 
the battery will depend on the grade of the cells and their care. If direc¬ 
tions are followed it will not be necessary to replace all of the cells at one 
time. See “Care of Dry Cells.” 

How can worn out cells be detected? 

1. By testing all cells with a reliable ammeter at least once a week 
and replacing those which show a low discharge (not less than 2 or 4 am¬ 
peres when discharged continuously for five seconds) with fresh cells. 

2. By observing the condition of the paste board casing of each cell. 
If moist or wet, the cell should be replaced immediately as it will short 
circuit and spoil adjacent cells, also dry out and become useless. In any 
event such a cell will make the whole series, in which it is connected, in- 
eff active. 

How can the battery of a common battery exchange be used for oper¬ 
ating the Harmonic Converter? 

1. By using the extra or duplicate exchange battery if the exchange 
is so equipped. A switch can be provided so that the battery, not connect¬ 
ed to the switchboard, can be used for operating the Harmonic Converter. 
See Figs. 537 and 538 under the heading “Battery Reversing Circuits. 

2. By using the exchange battery direct with our “Noise Killer” to 
prevent disturbances in the exchange talking circuits. 

What constitutes a “Noise Killer •” for a common battery Harmonic 
Converter? 

A retardation coil and auxliliary battery, the former preventing the 
vibrator noise from affecting the switchboard talking circuits and the lat¬ 
ter supplying the portion of the current choked out by the retardation 
coil so that the Harmonic Converter will operate at full efficiency. Sea 
“Talking Battery Noise Killer.” 


HARMONIC PARTY LINE SYSTEMS 439 

7 can ^ ie wear on M ie contacts of the Harmonic Converter he 

lessened? 

By reversing the connection of the operating battery periodically 
so that the current will flow in reverse directions and thereby re-deposit 
^ j P] a ^ n H m w hich is electrically eaten away from the positive contacts 
and deposited on the negative contacts. See “Battery Reversing Cir¬ 
cuits.” 

2. By systematically inspecting and caring for the contacts. Never 
allow bad sparking to exist as it will not only wear away the contacts but 
cause the Harmonic Converter to give an inefficient ringing current, one 
which will not ring the bells properly and cause noise in the line circuits. 
See “Care of Platinum Contacts” and “Adjusting Vibrator Contact 
Screws.” 

How often must the operating battery of the Harmonic Converter he 
reversed to equalize contact deposits? 

Once every twenty-four hours, preferably the first thing in the morn¬ 
ing. 

How often must the Harmonic Converter he inspected? 

The condition of the contacts should be observed at least once each 
week, when the Harmonic Converter is not running, and if necessary any 
roughness removed from their surfaces. See “Care of Platinum Con¬ 
tacts.” 

A glass cover is provided over the vibrators so that their condition 
can be determined at all times when the Harmonic Converter is in opera¬ 
tion. It would be well to observe the condition of the vibrators through 
this cover several times each day and if any of the contacts show undue 
sparking to remedy the cause at once. 

What are the voltages of the ringing current delivered by the type of 
Harmonic Converter covered by these instructions? 

If the operating battery is at normal voltage (about 22 volts) the 
ringing currents will be as follows: 

No. 1 33 1-3 cycles 105 volts, No. 3 66 2-3 cycles 175 volts, 

No. 2 50 cycles 135 volts, No. 4 16 2-3 cycles 85 volts. 

Some of the first Harmonic Converters were made with lower 16 2-3 
cycle voltage (about 60 volts). The higher voltage was adoDted to assist 
in the ringing of the regular bn'd^in" or rural line subscribers and all Har¬ 
monic Converters now are provided for this service. 

Will this voltage ringing current break down insulation? 

If the proper ringing protection is provided in each of the ringing 
leads from the Harmonic Converter to the operators’ positions no trouble 
will be experienced. Care should be taken never to allow the Harmonic 
Converter to get out of adjustment, also to keep the voltage of the operat¬ 
ing battery as near normal as possible. 

What frequency ringing currents gives best results on ordinary 
bridging lines? 

The 16 2-3 or No. 4 ringing current is best adapted for regular bridg¬ 
ing bells. The higher frequencies are too rapid to allow the bell tapper to 
respond unless the latter is given a delicate adjustment. 


440 TELEPHONOLOGY 

What is the best frequency ringing current for common battery tele¬ 
phones ? 

The 33 1-3 cycle ringing current will give the best results as the bells 
in this case are in series with condensers which assist in their action. 

How can the Harmonic Converter be made to ring code signals satis- 
factorily on rural lines ? 

By keeping the 16 2-3 cycle vibrator operating continuously so that 
no time will be lost in waiting for its armature to get into full motion. 
See “Code Signal Ringing Circuit Connections” for diagrams. 

What is the proper protection for the ringing leads extending be¬ 
tween the Harmonic Converter and each operator's position? 

1. Protection relays which act as self-restoring automatic overload 
circuit breakers. There must be four for each operator, one located in 
each ringing lead. 

2. Incandescent lamps of 16 C. P. 110 volt rating can be used in 
place of the protection relays. Never use a bell, buzzer, ringing pilot or 
other inductively wound device on the ringing circuits as the standard 
Harmonic Converter is not designed for such conditions. Always consult 
the factory before placing any special equipment in the ringing circuits. 
Otherwise we cannot guarantee the successful operation of the system. 



Fig. 522a. Dean Ringing Protection Relay. 


GENERAL TROUBLE TEST. 

Vibrator Armature Fails to Run: 

1. See if motor contact “makes” properly as per “Adjusting Vibra¬ 
tor Contact screws.” 

2 . Test fuse No. 5 in Harmonic Converter and replace if defective. 

3. Test battery for voltage and output and if necessary put in good 
condition. 

4. Trace circuit as per diagram and remove defects if any exist. 

Vibrator Armature Pulls up against Pole Pieces but does not Vibrate: 

1. See that vibrator contact screw “e” breaks contact with its spring 
“s” when the armature is pulled up against pole pieces. See “Adjusting 
Vibrator Contact Screws.” 

2 . Test vibrator windings for grounding on core. Replace if defec¬ 
tive. 



HARMONIC PARTY LINE SYSTEMS 441 

Inspect vibrator winding terminals and connecting wires and see 
that they are not in contact with cores or frame of vibrator. 

I ibrator Armature runs but no Ringing Current: 

.. ■, Test fuses Nos. 1, 2, 3 and 4 in Harmonic Converter and replace 
if defective. 

2. See that battery is properly connected to “BP” binding post of 
Harmonic Converter as per diagram. 

3. If starting relay is used see that it is connected properly in cir¬ 
cuit as per diagram, also that its armature is pulled up when making test 
for ringing current. 

4. If retardation coil and auxiliary battery (constituting a Noise 
Killer in common battery exchanges) is used see that the latter is of prop¬ 
er voltage and output and connected as per diagram. 

5. See that pole changing contacts a, b, c and d of vibrator are prop¬ 
erly adjusted as per “Adjusting Vibrator Contact Screws.” 

Vibrator Operates but Ringing Current Weak: 

1. See that voltage of battery is normal, about 22 volts, and of suf¬ 
ficient output. If dry battery is used, see “Care of Dry Cells.” 

2. If a common battery “Noise Killer” is used, test the auxiliary 
battery for voltage and output and if made up of dry cells, replace with 
fresh ones when the output is less than 4 amperes. See “Care of Dry 
Cells.” 

3. See that pole changing contacts a, b, c and d of the vibrator are 
properly adjusted as per “Adjusting Vibrator Contact Screws.” 

4. Remove all “buzzers” or ringing pilot relays from the ringing 
circuits, such as coils, condensers or broken down insulation in keys and 
wiring. 

5. See that no leakage exists through apparatus bridged across the 
ringing circuits, such as coils, condensers or broken down insulation in 
keys or wiring. 

Converter Operates but Fails to Ring Harmonic Bells: 

1 . See that the conditions under the preceding heading are fulfilled. 

2. Test each frequency vibrator for proper rate of vibration by one 
of the methods mentioned under heading “Frequency Testing and Adjust¬ 
ing” and if necessary, change position of weight on vibrator armature. 

3. Be sure that Harmonic bells are in proper adjustment, or in 
other words, have not been readjusted since leaving the factory. 

Harmonic Bells Cross Ring : 

1. Test battery for proper voltage which is about 22 volts normal 
and not less than 20 volts or over 24 volts. See “Battery Reversing Cir¬ 
cuits” for suggestions regarding battery wiring. 

2 . Have each frequency of the vibrator inspected as per instruct'ons 
for “Frequency Testing and Adjusting” and “Adjusting Vibrator Contact 
Screws.” 

3. Test the five generator leads extending from the Harmonic Con¬ 
verter to the switchboard for crosses between same, also, if Harmonic 
Converter is being tested or the first time after installing, be sure that 
the proper wire is used for the “common” (marked G or GS in d ; ag am) 
instead of one of the “frequency” wires (marked 33, 50, S6 and 16 in 
diagram. 





442 


TELEPHONOLOGY 


4. Be sure that the harmonic bells are properly adjusted and have 
not been changed or readjusted since leaving the factory. 

Motor Contact Sparks: 

1. See that operating battery voltage is within its proper limits, 20 
to 24 volts. 

2. Inspect contacts “e” and “s” for roughness and if necessary 
clean as per “Care of Platinum Contacts.” 

3. See that the adjustment of contact screw “e” is properly made as 
per “Adjusting Vibrator Contact Screws.” 

4. If following the above instructions fail to kill spark, br'dge the 
motor contacts with a non-inductive resistance coil and condanser as per 
“To Prevent Spark at Motor Contacts.” 

Pole Changing Contacts Spark: 

1. See that the operating battery voltage is within its proper limits. 
20 to 24 volts. 

2. Have vibrator armature movement sufficient to break ard make 
pole changing contacts properly. See “Adjusting V brator Contact 
Screws” and “Adjusting Motor Contacts.” 

3. Inspect pole changing contacts a, b, c and d for roughness of sur¬ 
faces and clean as per “Care of platinum Contacts” if necessary. 

4. See that adjustment of contact screws a, b, c and d are properly 
made as per “Adjusting Vibrator Contact Screws.” 

5. See that no leakage exists through apparatus bridged across the 
ringing circuits such as coils and condensers or broken down insulation in 
keys and wiring. 

6 . If following above instructions fail to remedy sparking then test 
condensers used across transformers for faults such as open or short cir¬ 
cuits, also too high or low capacity. 

Ringing Noise in Line Circuits: 

1. Inspect adjustment of Harmonic Converter vibrator as per “Care 
of Platinum Contacts” and “Adjusting Vibrator Contact Screws.” 

2. Test auxiliary battery of “Noise Killer” if used, for proper volt¬ 
age and output and if made up from dry cells, replace when the output is 
lower than four amperes. Also test retardation coil of “Noise KiMer” for 
short circuited winding by bridging with a telephone receiver when Con¬ 
verter is in operation. If coil is 0. K. a buzz will be heard. 

3. If lines are metallic, trouble may be due to improper trans osi- 
tion or lack of transposition. 

4. If lines are properly transposed, unbalancing due to leakage to 
earth will cause trouble. Have tree leakage cleared, also low insulation 
repaired. 

5. Grounded or common return lines are noisy with all kinds of 
ringing current, more so with the higher frequencies. The only reliable 
remedy is to make line metallic and transpose. 

Buzzing Noise in Talking Circuits of Common Battery Switchboard: 

See No. 1 and 2 under “Ringing Noise in Line Circuits.” 

3. Defective insulation in switchboard wiring, wet cables and dust 
between key springs sometimes cause generator noises. 

4. Some common battery switchboard circuits are unbalanced, and 
require special wiring to prevent generator noises. In a few cases, the de- 


HARMONIC PARTY LINE SYSTEMS 


443 


sign of the switchboard circuits are defective so that some noise will al¬ 
ways be induced to the talking circuits regardless of the kind of ringing 
machine used. 

ADJUSTING VIBRATOR CONTACT SCREWS. 

The adjusting of the Harmonic Converter springs and screws is a 
very simple operation but it must be done properly to obtain the highest 
efficiency as well as prevent sparking at the pole changing contacts. The 
Harmonic Converter is shipped from the factory with the best adjustment 
of these contacts and by observing this original adjustment it will be seen 
that the middle spring “s”, Fig. 523, makes contact with its platinum 
screw “e” and that the four ends of the springs 1, 2, 3 and 4 just clear 
their respective contact screws b, a, c and d. This is when the vibrator 
armature is at rest. 





Fig. 523 


All of the necessary adjustment of the contacts is done by turning the 
platinum screws in or out of their mounting posts as the case might re¬ 
quire. The clamping screws A. B. C. D and E are provided to hold the 
platinum screws from loosening when the Harmonic Converter is in oper¬ 
ation. Thus, before adjusting a platinum screw, the clamping sc ew 
should be loosened and after the adjustment is complete the same should 
be tightened so that the platinum screw cannot be turned with the fingers. 

Adjusting Motor Contact. —The contact between the middle spring 
“s” and its screw “e”, Fig. 523, is in the portion of the Harmonic Conver¬ 
ter circuit which makes that particular vibrator operate. This contact 
must be made when the vibrator is at rest, the same as a house bell or buz¬ 
zer. The proper adjustment is obtained by turning this screw “e” in 
against the spring “s” until the place is reached where the vibrator will 
not start to vibrate when the operating battery is switched on and the 
voltage of the latter is at its lowest limit, about 20 volts for a standard 
Harmonic Converter. Before starting to adjust contact “e” remove fuses 
Nos. 1, 2, 3 and 4 found on connecting rack of the Harmonic Converter. 
Fuse No. 5 is in the vibrator circuit and must not be removed in this test. 
Now turn the screw “e” back about one-eighth turn and test the starting 
of the vibrator by again switching on current. I the vibrator does not 
start promptly, it will be necessary to turn the screw “e” back another 
one eighth turn. Test as before for starting. In this way the vibrator 
armatures can be adjusted readily for an extreme movement, but its move¬ 
ment should not be sufficiently great to make the armature hit the pole 
pieces of the magnet when vibrating with the battery voltage at its maxi¬ 
mum (about 27 volts for a standard Harmonic Converter unless end cell 
switches are used as elsewhere explained, then 24 volts will be maximum). 
Thus, in order to have a safe adjustment, switch on the operating battery 



















444 


TELEPHONOLOGY 


when it is at its highest voltage (on a storage battery this will be when 
the cells are being charged and on a dry cell outfit when the dry cells are 
new and the Converter is just set up, as described under “Battery Revers¬ 
ing Circuits”), and if the vibrator armature hits the pole pieces, turn back 
the platinum screw “e” until the armature just clears the end of the mag¬ 
net in its vibration. Be sure that the contact spring “s” rests firmly 
against its stop at its free end before making the adjustment with the 
platinum screw. After the vibrator armatures are adjusted so as to start 
when the operating current is switched on, at both low and high voltage 
limits—test for proper rate of movement as per “Frequency Testing and 
Adjusting”—then replace the fuses Nos. 1 to 4 inclusive and proceed with 
the following adjustments. 

Adjusting the Pole Changing Contacts .—The four outside contacts 
1, 2, 3 and 4 of a Harmonic Converter vibrator serve to switch the direct 
current to the primary winding of the transformer so as to flow through 
the latter in one direction, and on the return movement of the armature, 
to break this circuit and substitute another connection so that the direct 
current will flow through the same transformer winding in a reverse di¬ 
rection. This complete reversing of the direct current is maintained as 
long as the battery is connected to the Harmonic Converter and the vibra¬ 
tor is in motion, thus producing an alternating current for ringing pur¬ 
poses. It will be seen that these four contacts must make and break the 
full strength of the current used by the entire exchange for its particular 
frequency and if allowed to spark continuously will cause trouble. 

To get the proper adjustment of these four pole changing contacts 
have the vibrator armature and motor contact adjusted as previously de¬ 
scribed, then proceed as follows: 

See that the contact springs 1, 2, 3 and 4 rest firmly against their re¬ 
spective stops at their free ends. This adjustment is made right when 
the vibrator is assembled at the factory and should never be disturbed un¬ 
less new springs are to be put in place, the latter operation being describ¬ 
ed under the heading “Replacing Platinum Contacts.” 

It is advisable to adjust one of the contacts (a, b, c, or d) at a time by 
first turning it through its supporting post so that its end will just touch 
its platinum contact spring and then turning back the proper amount to 
leave a small separation between the platinum surfaces. This contact sep¬ 
aration is not the same for the different frequency vibrators and must be 
made as subsequently described and indicated in the following table if the 
best results are to be obtained. 


Vib. 

Freq. 

No. 1 

33 eye. 

No. 2 

50 “ 

No. 3 

66 “ 

No. 4 

15 “ 


Front 
Contacts 
0.0130” b & d 
0.0086” b & d 
0.0060” b & d 
0 .0200” b & d 


Back 
Contacts 
0.0130” a & c 
0 .0110” a & c 
0.0095” a & c 
0.0150” a & c 


It will be seen that the contact separations are the same for all four 
screws in the 33 cycle vibrator, while in the 50 and 66 cycle vibrators the 
separations between the front contacts are smaller than between the back 
contacts. The 16 cycle vibrator contact separations are smaller for the 
back contacts than for the front. 


HARMONIC PARTY LINE SYSTEMS 


445 


These contact separation distances can be obtained by using a “slip 
guage” of the proper thickness, but a more convenient method is to turn 
the platinum screws back the proper amount after setting them up 
against the platinum springs as just described. A complete turn of a plat¬ 
inum screw will give a separation of 1-32 of an inch (.031) between the 
platinum contacts as the thread is 32 to the inch. Now by turning the 
screws back as indicated separation can be obtained very accurately. 


Contact 


Vib. 


Freq. 

Screws 


Turn Back 

No. 

1 

33 

Front 

b 

& 

d 

150°, not quite 1/2 turn 

No. 

1 

33 

Back 

a 

& 

c 

150°, not quite 1/2 turn 

No. 

2 

50 

Front 

b 

& 

d 

100 °, slightly over 14 turn 

No. 

2 

50 

Back 

a 

& 

c 

125°, slightly over 1-3 turn 

No. 

3 

66 

Front 

b 

& 

d 

70°, slightly over 1-3 turn 

No. 

3 

66 

Back 

a 

& 

c 

110°, between 1-4 & 1-3 turn 

No. 

4 

16 

Front 

b 

& 

d 

240°, or just 2-3 turn 

No. 

4 

16 

Back 

a 

& 

c 

170°, not quite 1-2 turn. 


Be sure that for each vibrator both back contacts “a” and “c”, Fig. 
523, are adjusted so as to have the same separation, also that both front 
contacts “b” and “d” have the same separation. As soon as the contacts 
on the four vibrators are adjusted the fuses Nos. 1, 2, 3 and 4 can be re¬ 
placed and the current connected to the Converter. If the contact adjust¬ 
ments are made properly, no sparking will exist when the vibrators are 
operating. However, if any should show, due to a slight inequality in the 
contact separations, (other parts of the Converter having been previous¬ 
ly inspected according to instructions) it can be cleared up by a slight 
movement (not more than 1-6 of a turn in either direction) of one or the 
other of the front platinum screws “b” or “d”, the adjustment being made 
with the vibrators in motion. In the latter adjustment, be sure not to 
move the screws more than 1-6 turn either way as a short circuiting of the 
contacts may result which will blow the Harmonic Converter fuses and 
possibly melt the platinum contact surfaces together. 

I r the Harmonic Converter platinum contacts should become fused 
together due to an accidental short circuiting, they can be separated by a 
knife blade, driving it between the contacts by a light sharp blow. After 
separating, clean the surfaces as explained under “Care of Platinum Con¬ 
tacts.” 

The Harmonic Converter now should be tested for proper fre¬ 
quency, voltage and output as explained under the headings “Frequency 
Testing and Adjusting” and “Voltage Testing Apparatus.” 

FREQUENCY TESTING AND ADJUSTING. 

The reeds or moving parts of the Harmonic Converter vibrators are 
made so that they will last indefinitely and vibrate uniformly without a 
perceptible change in rate of operation. However, a different adjustment 
in the contact springs or wearing away of the platinum will sometimes al¬ 
ter the speed so that we provide a means for readjusting. Thus, the 
weights, found at the lower ends of the vibrator armatures, are provided 
with set screws so as to be raised or lowered. Raising the weights in¬ 
creases the rate of vibration. Lowering the weights decreases the rate. 


446 


TELEPHONOLOGY 


Before making a change in the adjustment of the weights, be sure 
that the Harmonic Converter is operating properly in every other way; 
that the voltage of the battery and the voltages o,' the ringing currents 
are normal; that the vibrators are moving their full amount and that all 
of the platinum screws are properly adjusted. Also, have some means at 
hand for testing the frequency of the ringing current so that it will be 
known when the reeds are vibrating properly. 

There are several types of frequency meters on the market which can 
be used in making this adjustment, but if not available, a set of four ac¬ 
curately tuned harmonic ringers will serve the purpose. These standard 
ringers should be mounted on a rigid support and wired across a pair of 
line wires with a 1 M. F. condenser in series with each bell. A 5,000 ohm 
non-inductive resistance should be placed in series with one of the line 
wires so that all ringing current to the bells must pass through the same. 
(See Fig. 524 for proper wiring). This resistance cuts down the ringing 
current to such an extent that none of the bells will respond unless the 
ringing currents are exactly in tune with the natural period of vibration 
of the bells. 



Sooo OHM 
NOS- IHOi/CTlvC 
RESUTAh/CC 


If, upon test, it is found that none of the standard bells will respond 
to its corresponding ringing current, it is evident that the vibrator is not 
operating at the correct speed. 

Now, upon touching the tapper of the standard bell, (when ringing 
current is applied) it is possible to make it ring, or at least accelerate the 
movement of its tapper, the vibrator is running too fast to operate the bell. 
Otherwise, if the bell does not ring, the reverse is true and the vibrator is 
too slow. 

The speed of the vibrator then can be easily increased or decreased, 
as is necessary to ring the bell, by simply raising or lowering the weight 
on the end of the armature. 

In adjusting the lowest frequency vibrator (No. 4 party, 16 2-3 cycle) 
always have the weight placed as low as it will go and at the same time 
operate the standard bell through the 5,000 ohm test resistance. 

Before adjusting the armature weight be sure that a mark or scratch 
is made on the armature projection just below the lower end of the weight. 



























HARMONIC PARTY LINE SYSTEMS 


447 


This will allow the weight to be replaced to the same position if a better 
adjustment is not found. A mark of this sort is made after the final ad¬ 
justment by the factory Testing Department to show the original setting. 
In changing the weight for adjustment, it is better to do it with small 
movements, up or down on the armature, rather than by one big move¬ 
ment. This method may take several trials, but the correct position may 
be ascertained to a certainty and much quicker than by making a big 
movement of the weight to start with. 

It will be found an advantage to mount the standard adjusting bells 
in a permanent position and wire them through four keys to the Harmonic 
Converter as illustrated in the accompanying circuit. 

VOLTAGE TESTING APPARATUS. 

If no high resistance alternating current voltmeter (5,000 ohms at 
least) is available for testing the ringing current of the Harmonic Con¬ 
verter, very good results can be obtained by using a regular 24 volt 
switchboard lamp wired in series with the proper non-inductive resist¬ 
ances, as shown in Fig. 525. 


- VOLTAGE TEST 80X- 



GOHHlCJiKt RACK 


Fig. 525. 



6i 33 

So & 

tc *- To converter ifo. 1 

4 

4 4 

4 4 

4 

w-0 

0-6S 33-D 


Q-wtotest box 

¥ 

f ¥ 

f ¥ 

? 

BK 

6s a 

50 66 

16 - TO CONVERTER No i 


THRU QPOT 6»BY KNIFE SWITCHES 


Fig. 526. 


It is absolutely essential that these resistances be wound non-induc- 
tively and that the entire spool be boiled in paraffine or bees-wax or insu¬ 
lated with armature varnish. 

The resistance of the non-inductive windings should be as follows. 


For No. 1 Frequency 33 cycle use 750 ohms 
“ No. 2 “ 50 “ “ 1050 

“ No. 3 “ 66 “ “ 1450 

“ No. 4 “ 16 “ “ 550 


Res. 
» < ‘ 


<< 


(A) 

(B) 

(C) 

(D) 


The lamp should burn at full briliancy when connected to the proper 
frequency by pressing the corresponding button. For example, to test the 
33 cycle ringing current button No. 1 is pressed, etc. Button marked B 
fs fo y r testing the voltage of the battery used in operating the Harmonic 
Converter. If the lamp does not show full briliancy when button B is 
depressed, it is an indication of a weak battery and the latter will need 
immediate attention. It would be well to test the battery in this way be¬ 
fore testing the voltage of the ringing currents as it will be impossible to 
get full strength of the latter if the battery is low in voltage. 

The keys, resistance coils and switchboard lamp can be ™untedina 
small box and located near the Harmonic Converter and wired permanent- 
















448 


TELEPHONOLOGY 


ly to it. If there are duplicate sets of Harmonic Converters, three double 
pole double throw baby knife switches can be wired into the circuits ex¬ 
tending from the Harmonic Converter to the voltage test box, so that one 
box will serve for both Harmonic Converters. This wiring is indicated 
in Fig. 526. We can furnish these voltage test boxes completely wired, 
also the necessary six wire twist power cable for connecting the same to 
the Harmonic Converters. These test boxes can be readily made or as¬ 
sembled by the Telephone Company and in this event, we can furnish the 
separate parts, such as the four resistance spools and switchboard lamp 
with socket. When ordering the voltage test box or parts of the same, 
give the serial number of the Harmonic Converter. 

CARE OF PLATINUM CONTACTS. 

The pole changing and vibrator operating contacts of the Harmonic 
Converter are made from platinum securely riveted into the contact 
springs and adjusting screws. With very little attention these contacts 
will do all of the work required of them and last many years. 

To prevent unnecessary waste of platinum and also to give the most 
efficient operation of the Harmonic Converter, it is essential that the ma¬ 
chine be adjusted so that the contacts will not spark. A slight sparking 
when ringing a large number o bells is sometimes difficult to avoid, but 
as the sparking then is of short duration, it will not cause trouble. 

The continual opening and closing of the circuit at the contacts of the 
Harmonic Converter will in time cause the positive ( + ) contact to be¬ 
come blackened and to loose platinum and the negative (—) contact to be 
whitened and to receive a deposit of the platinum lost from the positive 
contact. Thus, depressions or pits will be formed in the positive contacts 
and corresponding tips, or built up portions, in the negative contacts. For 
example, if the positive and negative poles of the battery are connected to 
the contacts of the Harmonic Converter as shown in Fig. 527, then the 
points a, d, 1, 3 and 5 will be eaten away and the corresponding points 2, 
4, b, c and e will be built up. 


F~/ G-. S2. 1 



By properly wiring the battery so as to allow its connections to the 
Harmonic Converter to be reversed at least once a week, it will be possible 
to cause the platinums to deposit in the opposite direction and partially 
overcome this trouble. (See “Battery Reversing Circuits”). However, a 
rough pair of contacts will have a tendency to spark and if left in this con- 



























HARMONIC PARTY LINE SYSTEMS 


449 


dition the pits in the platinum will become very deep and eventually neces¬ 
sitate a complete replacement of parts. Figs. 528 and 529 show enlarged 
views of a pair of contacts which have been subjected to sparking, the 
second view showing the result when the sparking is allowed to continue 
for some time. The contacts should never be allowed to get in either of 
these conditions. 

As soon as the surfaces of the contacts becomes roughened, it is time 
to file or dress them off smooth. This process may be necessary once a 
week. In dressing off the platinums use a “dead smooth” file with a flat 
surface. This file should also be thin so as to be readily drawn between 
contacts as illustrated in Fig. 530. 

If a file is not available, use emery cloth of the finest grade stretched 
over a thin, flat piece of wood or metal as illustrated in Fig. 531. Before 
using this tool, its surface should be rubbed over an iron bar or other hard 
material so as to render the emery less harsh and prevent roughening the 
platinum. Always use a file for this work when possible. 

If the contacts are badly pitted, it will be necessary to remove enough 
of the platinum to reach a smooth surface. This is indicated in the cases 
shown in Figs. 528 and 529 by the dotted lines. 

The file (or emery cloth) should be drawn between the platinum 
contacts with a light free motion, care being taken to keep the file straight 
and square with the end surfaces of the platinum. In other words, when 
the platinums are dressed up smooth, their end surfaces should be parallel 
as shown in Fig. 532 so as to give the largest possible area of contact be¬ 
tween them. If it is difficult to do this properly, then slightly round the 
end of the platinum in the screw but always keep the platinum in the 
spring with a flat smooth surface. See Fig. 533. 

REPLACING PLATINUM CONTACTS. 

When it becomes necessary to replace the platinum contacts of our 
Harmonic Converter new platinum pointed springs and new platinum 
pointed screws can be readily substituted for the defective ones. 



DOUBLE 

CONTACT 

SPRING 

AP*2t36 „ 


A«MATUftf 
3 /P* 2UZ 

--A 



CIRCUIT > 

connection ' ' 

P*2143 

P *3*08 

MOTOR CO NT AC 
MOUNTING 

SPRING STOP 
p *mi 

STOPS 

AP 2336 ^ -<=^— 

ARTS ASSEMBLED SS 


■ iNsuL/moii 

P*iW 





i -STOP 

tr MOTOR 
CONTACT 
SPRING 

AP'ZiSI 


PiUt 


Figs. 533a. 534, 535, 536. 

29 











































450 


TELEPHONOLOGY 


The five adjustable contact screws on each vibrator are Removed by 
first loosening the clamping screws in the tops of their respective posts. 

The middle or motor contact spring is removed by taking out the 
screws c and d, Fig. 533a. 

The two springs holding the four outside or pole changing contacts 
are removed by first taking the complete armature off the vibrator frame. 

This is accomplished by removing the lock nuts marked “a” and screws 
“b”, Fig. 533a. These contact springs are securely held in place by the 
screws “g” and “h” and luck nuts “e” and “f”. When replacing these 
parts be sure to arrange them in their proper positions as illustrated in 
Fig. 534 and clamp them securely with the screws “g” and “h”. The lock 
nuts “e”, “f” and “a” are used solely to keep the screws from loosening 
and therefore must be set tight. 

All of the contact springs on the Harmonic Converter are provided 
with stops to limit their movements in one direction. The contact springs 
should have a slight initial tension against these stops when not in contact 
with their respective platinum screws. In other words, the springs 
should normally rest lightly against the stops. 

When assembling the contact springs see that their ends are slightly 
bowed as indicated in the upper view of Fig. 535. Then when the springs 
are clamped in place between the stops, the proper initial tension against 
the latter will be had. If this tension is found to be too great, after the 
springs are clamped in place, it can be reduced by forcing the contact 
spring back into the position indicated by the dotted lines “a” and “b”, 
Fig. 535. 

The middle or motor contact spring, shown in Fig. 536, should have a 
fairly strong initial tension against its stop, more so than the pole chang¬ 
ing springs. 

The proper separation between the platinum screws and contact 
screws is given under the heading “Adjusting Vibrator Contact Screws.” 

BATTERY REVERSING CIRCUITS. 

Under the heading “Care of Platinum Contacts” attention is called to 
the action of direct current on the platinum contacts of the Harmonic 
Converter, the material of the surface of one contact gradually eating 
away and becoming deposited on the surface of the opposite contact. As 
this action is not uniform for the entire surface of the contacts a rough¬ 
ness will result which has a tendency to cause sparking. We have found 
that if the battery is reversed periodically this depositing action can be 
practically neutralized, the platinum deposited on one contact being re-de- 
posited on the opposite contact, etc. In order to be effective this reversing 
should be done at least once every twenty-four hours, preferably the first 
thing in the morning. 

Battery Reversing Circuits—One Converter—One Storage Battery .— 
Fig. 537 illustrates the wiring of our Harmonic Converter when operated 
by one storage or constant current battery. In this case the storage bat¬ 
tery is one which is not used for furnishing talking current for the switch¬ 
board circuits, and can be eleven small size cells such as “PT Chloride Ac¬ 
cumulator.” The switches shown in this circuit are as follows: 


HARMONIC PARTY LINE SYSTEMS 451 

Switch No. 1—Four Pole, Single Throw. Lever up—Connects Converter 
to Switchboard. 


Switch No. 2—Double Pole, Single Throw—Fused. Lever up—Starts 
Converter. 


Switch No. 4—Double Pole, Double Throw, Lever down—Battery direct. 
Lever up—Battery reversed. 

Switch No. 5—Single Pole, Double Throw, Lever up—Normal position, 11 
cells, Lever down—Charging position—9 cells. 



Switches Nos. 1 and 2 make it possible to test and adjust the Har¬ 
monic Converter without removing the wires from the connecting rack. 
Switch No. 4 does the reversing of battery as previously described so as 
to equalize the wear on the contacts. Switch No. 5 is arranged so that the 
Harmonic Converter can be operated from nine cells when the battery is 
being charged, thus keeping the voltage practically uniform at all times. 

The Harmonic Converter is designed to operate from eleven cells 
regardless of the charging periods, but it will be found that a higher 
efficiency can be obtained by keeping the voltage of the current, supplied 
for its operation, at about 22 volts. This will allow the vibrators to be 
adjusted for a small range in voltage and not require as close attention as 
the wider range of adjustment. The use o ' the end cell switch No. 5 for 
this purpose will cause no inconvenience as it is always set so as to con¬ 
nect nine cells when charging the storage batteries and immediately when 
the charging is stopped, it is thrown to the normal or eleven cell position. 
This operation will give all of the cells practically the same wear, as cells 
Nos. 10 and 11 receive the same discharge as the remaining nine cells. 

Battery Reversing Circuit—Duplicate Converters—One Storage Bat¬ 
tery. —Fig. 538 shows a modification of Fig. 537 in that a duplicate set of 
Harmonic Converters is used. Here it is necessary to make switch No. 1 
of double throw construction so that ringing current from only one Har¬ 
monic Converter can be connected to the switchboard, the leads to the 
other Harmonic Converter being automatically cut off when the switch is 
thrown. Separate starting switches Nos. 2 and 3 can be provided for 




































452 


TELEPHONOLOGY 


each Harmonic Converter so that the machines can be started and oper¬ 
ated independently of each other. This will allow each machine to be 
inspected and adjusted when the other is furnishing current for the 
exchange. Switches Nos. 4 and 5 are the same as in Fig. 537. The 
switches for this complete circuit will be as follows: 

Switch No. 1—Four Pole, Double Throw, 


Lever up—Connect Converter No. 2 to Switchboard, 
Lever down—Connect Converter No. 1 to Switchboard. 

Switch No. 2—Double Pole, Single Throw, fused 
Lever up—Starts Converter No. 1. 

Switch No. 3—Double Pole, Single Throw, fused 
Lever up—Starts Converter No. 2. 

Switch No. 4—Double Pole, Double Throw, 

Lever up—Battery Direct, 

Lever up—Battery reversed. 

Switch No. 5—Single Pole, Double Throw, 

Lever up—Normal position, 11 cells, 

Lever down—Charging position, 9 cells. 


If a duplicate set of storage batteries are available for operation of 
this circuit, an additional switch will be necessary and should be wired 
the same as switch No. 6 in Fig. 540. This switch No. 6 is a double 
throw and when its lever is in the “up” position it connects ex¬ 
change battery No. 1, and when in the “reversed” position exchange bat¬ 
tery No. 2. The connection of all of the other switches from Nos. 1 to 5 
inclusive remain the same as just described. 


Battery Reversing Circuits—Duplicate Converters Noise Killer—One or 

Two Storage Batteries. 


When a retardation coil and auxiliary battery are used for prevent¬ 
ing noise on the talking circuits of the switchboard as explained under 
the heading “Talking Battery Noise Killer” a circuit as shown in Fig. 540 
should be used. This circuit is for a duplicate set of Harmonic Conver¬ 
ters and a duplicate set of storage batteries. The functions of the vari¬ 
ous switches are the same as explained in Fig. 538 and consist of the fol¬ 
lowing : 


Switch 

Switch 

Switch 

Switch 

Switch 

Switch 


No. 1—Four Pole, Double Throw, 

Lever up—Connect Converter No. 2 to switchbord. 
Lever down—Connect Converter No. 1 to switchboard. 
No. 2—Three Pole, Single Throw—Fused, 

Lever up—Start Converter No. 1. 

No. 3—Three Pole, Single Throw—Fused, 

Lever up—Start Converter No. 2. 

No. 4—Four Pole, Double Throw, 

Lever down—Battery direct. 

Lever up—Battery reversed. 

No. 5—Single Pole, Double Throw, 

Lever up—Normal position—11 cells, 

Lever down—Charging position—9 cells. 

No. 6—Double Pole, Double Throw, 

Lever up—Converter on exchange Battery No. 1, 

Lever down—Converter on exchange Battery No. 2. 










HARMONIC PARTY LINE SYSTEMS 


453 


, , If ,°, 1 ? ly 01 ? e exchange battery is used then switch No. 6 can be omit¬ 
ted and the wire from the outside terminal to cell No. 11 connected to the 

N P rS e q C Q °n n i a i C n t0 swlt . ch , ^°; u 5 ? nd the wire from the point between cells 
Nos. 9 and 10 connected to the lower contact of switch No. 5. 



Battery Reversing Circuits—Dry Cell Converter. 

The reversing of the battery connections to the Harmonic Converter 
for equalizing the wear on the contacts can be had on the dry cell type 
by providing a single pole, double throw baby knife switch and wiring 
the same as illustrated in Fig. 541. 



Fig. 541. 






























































































454 


TELEPHONOLOGY 


Each of the battery trays should be wired with two sets of sixteen 
or eighteen dry cells (32 or 36 total cells in each tray) connected in series 
multiple. The positive (-(-) terminal of tray No. 1 and the negative (—) 
terminal of tray No. 2 are both connected to the GP binding posts of the 
Harmonic Converter, while the negative (—) terminal of tray No. 1 is 
connected through fuse No. 6 to the left hand contact of the reversing 
switch and the positive (+) terminal of tray No. 2 through fuse No. T to 
the right hand contact of the same switch. Now when the reversing 
switch lever is thrown to the right hand position, the upper tray is con¬ 
nected to the Converter circuit furnishing current in one direction and 
when the reversing switch lever is thrown to the left hand position, the 
upper tray is disconnected and the lower tray substituted, the operating 
current then being in a reversed direction. 

CARE OF DRY CELLS. 

A good dry cell can be made to give excellent results in connection 
with the Harmonic Converter as the current consumption of the latter is 
very small when connected to a switchboard in the proper manner. It is 
absolutely essential, however, that the dry cells be inspected often and all 
defective ones immediately removed and replaced with fresh cells. 

Most dry cells are protected with a pasteboard casing and the latter 
will absorb moisture if not kept in a dry place. This will cause a quick 
deterioration of the cell, especially when put in service, as a leakage of 
current will then exist between adjacent cells. 

Battery makers recommend that all surplus stock of dry cells be kept 
in a cool dry place, but not where they will freeze. The makers also call 
attention to the fact that a dry cell, when cold, will not show a full reading 
on a testing ammeter but will give good results when at a normal temper¬ 
ature. This, in itself, is sufficient reason for placing the Harmonic Con¬ 
verter and its dry cells in a room where uniform and normal temperature 
is maintained. 

When installing dry cells in a Harmonic Converter, be sure that each 
cell is of full rating by testing with a reliable pocket ammeter, or other 
current indicating device, and also reject all cells which have damp or 
moist pasteboard coverings. If an ammeter is used, each new No. 6 dry 
cell should show a discharge of at least 15 amperes when the ammeter 
connections are made direct with the terminals of the cell as shown in 
Fig. 543, and not fall below this amount when the discharge is maintained 
for about five seconds. Continuous discharge of this sort is rather severe 
on the cell and must not be maintained for any longer period. 

In making ammeter tests each cell should be tested separately and 
the ammeter connected directly across the metal binding poses of the cell. 
After the cells have been wired in the Harmonic Converter circuit, these 
tests can be made in the same way and without disconnecting the cells 
from the circuit. In all current tests have the ammeter firmly connected 
with the dry cell binding posts as a slight resistance in the contacts will 
cause a false reading—the needle then indicating a small current flow. 

If a voltmeter is used for testing, it will be necessary to discharge 
the dry cell through a low resistance (about two-hundredths of an ohm), 
such as can be obtained from a piece of No. 18 B. & S. gauge copper wire, 
3 ft. long, and at the same time measure the voltage across the terminals 
as shown in Fig. 542. In such a test, on new dry cells, the voltmeter 


HARMONIC PARTY LINE SYSTEMS 


455 


should give a reading of at least 1 volts when the current is discharged 
continuously through the copper wire for five seconds. An open circuit 
reading, made across the cell terminals but without any current discharge 
will give no indication of the condition of the cell. As a matter of fact, a 
completely worn out cell often will show full voltage reading on the high 
resistance voltmeter. This same cell will give practically no current and 
if left in a series of cells will destroy the effect of the whole series. 

When no measuring instruments are at hand a rough test for deter¬ 
mining the output of a dry cell can be made by observing the heating ef¬ 
fect of a piece of wire. For example; a 12 inch piece of about No. 30 B. 
& S. gauge copper wire held across the terminals of a fresh cell, as shown 
in Fig. 544, should heat up so as to be almost too warm to hold. If the 
current discharge maintains the same heat after the wire has been held 
against the terminals for five seconds, this cell can be considered good. 
This is an emergency test only and is not recommended for regular use. 

While preliminary tests will allow poor cells to be discarded when in¬ 
stalling the battery yet these tests must not be considered final. Even in 
the best makes of dry cells local chemical action often will destroy their 
efficiency after being in use a few weeks. As has been stated before, one 
or more bad cells will spoil the complete series, and in the case of a multi¬ 
ple series one bad cell in each series will render the complete installation 
of dry cells inefficient. 

Therefore, we would recommend that the dry cells be inspected at 
least once a week, and all cells which show a loiv discharge be replaced 
with fresh cells of full rating. 

Also, all dry cells should be replaced which show wet or moist places 
in their pasteboard coverings. Such cells will dry out quickly and cut 
down the effect of the good cells, and in addition will cause a short circuit 
in adjacent cells and eventually ruin the complete set. 

If these instructions are followed carefully the Harmonic Converter 
will operate always at full efficiency and the cost of the battery renewals 
ivill be reduced to a minimum. Thus, it ivill not be necessary to replace 
all of the cells at one time. 

It will be found that the best results are obtained by using dry cells 
of the same make and size when for a series or series-multiple connection. 
In wiring the cells into the converter, great care should be exercised to 
see that the cells are properly connected together and to the converter. 
Heavily insulated copper wire, at least as large as No. 18 B. & S. gauge 
should be used for connection between the cells and from the battery to 
the converter circuit. The ends of these connecting wires should be 
scraped bright where they are to be held by the binding posts, care being 
taken not to nick the wire as a slight cut of this sort will be sure to cause 
break at some future time. Clamp the ends of the wires so as to avoid 
short circuits between adjacent cell terminals and connecting wires. 

New Cells should show an ammeter reading of at least 15 amperes at 
the end of five seconds, the meter being connected during the entire time. 

Old Cells—When in use dry cells will gradually become inefficient 
and should be discarded when they show an ammeter reading of less than 
2 amperes at the end of five seconds, the meter being connected during the 
entire time. 


456 


TELEPHONOLOGY 



Ammeter Tests. Figs. 542-43-44. 


In making this test have heavy wire “d” and wire to voltmeter “e” 
connected together permanently. Then connect “d” to one binding post 
of dry cell and other end of heavy wire “a” to other binding post of dry 
cell. After allowing the current to flow through heavy wire for five sec¬ 
onds, remove end “a” and immediately connect wire “b” so as to get read¬ 
ing on voltmeter. 



CODE SIGNAL RINGING CIRCUIT CONNECTIONS. 


It has been found from practical operation in a large number of ex¬ 
changes that a 33 1-3 cycle alternating ringing current is of too high fre¬ 
quency for the successful signaling on regular bridging or rural lines. 
Also, any frequency above 20 cycles is too fast to allow the regular bridg¬ 
ing ringers to respond properly, especially when the bells are of differ¬ 
ent makes and the lines heavily loaded or of short length and consequent- 








































































HARMONIC PARTY LINE SYSTEMS 


457 


ly low resistance. This requires that the 16 2-3 cycle ringing current of 
the Harmonic Converter be used for such service and it has been found to 
give execellent results. However, the 16 2-3 cycle vibrator is slow In 
starting, due to the low frequency, so that if a dry cell Converter is used 
and the same is started with the relay, it will be difficult to ring code sig¬ 
nals. If a master key is used and provided with a relay starting contact, 
the 16 2-3 cycle button can be depressed and held while the ringing of 
code signals can be done with the regular cord circuit ringing key. In 
this case the Harmonic Converter will not be running except when actual¬ 
ly ringing. 

Some operating companies prefer to sacrifice battery current for con¬ 
venience in signalling bridging lines and keep the 16 cycle portion of the 
Harmonic Converter operating continuously, at least during the busy part 
of the day. We show two circuits which will give this kind of service in 
connection with our standard Harmonic Converter. 


WHEN MASTER KEYS ARE USED. 


Fig. 545 shows a circuit arranged for use with master keys, the lat¬ 
ter being of special construction with an extra set of contacts on the end 
spring combination. The change in the Harmonic Converter is made by 
removing the two wires which run from the 16 cycle vibrator to the BP 
and BM binding posts of the Harmonic Converter connecting rack. The 




Fig. 545a. End and Side view, Dean Party Line Key. 


i 


ends of these wires are connected together and run to the middle point 
“a” of a single pole double throw baby knife switch. The upper contact 
“b” and the lower contact “c” of this switch are connected respectively to 
the upper rear binding post “ ” and upper binding post e of the start¬ 
ing relay. Now when the switch blade is in the “down . position ( a 
connected to “c”) the Harmonic Converter will operate m the regular 
way and the 16 cycle vibrator will be started by means of the relay thus 
consuming no battery current except when actually ringing. W thi the 
switch blades in the “up” position (“a” connected to b ) ard 16 cycle 
portion of the Converter will operate continuously so that the regulai 
lines can be rung with this frequency without depressing the master key. 
This circuit changing switch can be located in any conv *nient position, 
near the switchboard if thought advisable, so that He operator can have 
the 16 cycle vibrator operating continuously during rush periods and at 





















458 


TELEPHONOLOGY 


other times to reverse the connections so that battery current will not be 
wasted. The special apparatus required for this service are the master 
keys, as shown in Fig. 545a and the circuit changing Switch. 



Fig. 545b. Side view of Dean Key, showing Contact Springs. 

WHEN INDIVIDUAL KEYS ARE USED. 

Fig. 546 shows a modification of the circuit just described, which is 
designed for use when individual four or eight party ringing keys are 
provided in the switchboard. The two wires extending from the 16 cycle 
vibrator to the BP and BM binding posts of the Harmonic Converter con¬ 



necting rack are removed as in the previous case and are connected di¬ 
rectly to the upper binding posts “e” and “f” respectively of the starting 
relay. This change in wiring allows the 16 cycle vibrator to operate con- 






































































































HARMONIC PARTY LINE SYSTEMS 


459 


tinuously but without the 16 cycle transformer connected in circuit until 
a ringing key is depressed. Thus, the advantages of continual operation 
of the 16 cycle vibrator can be had without unnecessary waste of battery 
current, as the current required for operating this vibrator alone is almost 
negligible. 

No special apparatus will be necessary to provide for this method of 
operation. 

TO PREVENT SPARK AT MOTOR CONTACT. 

The amount of current broken at the motor contact of the Harmonic 
Converter is of such a small amount that sparking at this point does not 
occur unless the contact surfaces are in poor condition and improperly 
adjusted. However, external conditions often influence this portion of 
the Harmonic Converter so that a slight spark results. This spark is not 
of a destructive nature as long as the current is periodically reversed (see 
“Battery Reversing Circuits”) and the contacts kept clean (see “Care of 
Platinum Contacts”) 

The spark at the motor contacts can be done away with entirely by 
placing a condenser and a non-inductive resistance in series and across 
this portion of the vibrator circuit as shown in Fig. 547. A No. 6040 con¬ 
denser and a No. 6605 resistance coil should be used. The condenser and 
coil for each vibrator can be placed in the space directly below the slate 
vibrator base, care being taken to fasten them so as not to jar forward or 
interfere with the vibrator armature. 



/noTOft- 
CON TACT 

* e 



r /VOW-IND- 

KE^lSTA/xCE 
Coil_ 


Slate- $ a st¬ 
op VIBRATOR* 


Fig. 547. 


TALKING BATTERY NOISE KILLER. 


When the Harmonic Converter was designed one of the first prob¬ 
lems was the elimination of buzzing noises in the talking circuits of a 
common battery exchange, when the Harmonic Converter was operated 
from the same storage battery which furnished current to the switch¬ 
board. If the exchange has a duplicate set of storage batteries, switches 
can be provided so that the Harmonic Converter always can be operated 
from the battery which is idle, thus doing away with these buzzing noises 
and without the use of special apparatus. However, as this battery usual¬ 
ly receives a charge when not connected to the switchboard, special end 
cell switches should be provided as illustrated in Figs. 537 and 538 under 




























460 


TELEPHONOLOGY 


the subject “Battery Reversing Circuits” so as to keep the voltage of the 
current supplied to the Harmonic Converter, practically uniform, (about 
22 volts). 

Fig. 548 shows the theoretical arrangement of the “Noise Killer” 
circuit devised by the Dean Co. It consists of a special retardation coil 
of low resistance and high impedance and an auxiliary battery, the latter 
being connected between the coil and the Harmonic Converter. The use 
of a retardation coil alone will cut down the efficiency of the Harmonic 
Converter to a greater extent than it will cut down the buzzing noise in 
the switchboard talking circuits so that the auxiliary battery must be 
used to supply the momentary impulses of current which the retardation 
coil chokes out. The drain on the auxiliary battery is so slight that large 
size dry cells (No. 8) can be used for the auxiliary battery on small ex¬ 
changes, but for large common battery installations the auxiliary battery 
should be small storage cells. The latter cells need not be larger than PT 
size “Chloride Accumulators” for exchanges up to 6,000 lines. With a 
proper size retardation coil the storage cells will be charged automatically 
thereby requiring practically no care to keep them in proper shape. 

When dry cells are used for the auxiliary battery it will take thirty- 
four of the No. 6 size connected in series multiple, seventeen in each 
series, or if No. 8 size cells are used, one set of seventeen in series will do. 
If small storage cells are employed only ten will be required, one less than 
the eleven cells of the exchange storage battery used for operating the 
Harmonic Converter. This will allow the small cells to receive their 
charge directly from the exchange storage battery through the “Noise 
Killer” retardation coil. 



In connecting the auxiliary battery of the “Noise Killer” to the Har¬ 
monic Converter circuit great care must be taken in having it arranged 
so as to furnish current in the same direction as the exchange storage bat¬ 
tery, otherwise a short circuiting of the cells will result. See the accom¬ 
panying sketches. 

From the fact that the “Noise Killer” is designed to do away with the 
buzzing noise on the switchboard talking circuits, it is evident that any 
such noise may indicate trouble in the auxiliary battery. A poor auxiliary 
battery not only cuts down the operating efficiency of the Harmonic Con¬ 
verter but also causes the pole changing contacts to spark. Thus, a buzz¬ 
ing noise in the talking circuits or inefficient ringing will serve as an au¬ 
tomatic indication of worn out dry cells in the “Noise Killer” circuit (if 
dry cells are used)' or trouble in the small storage cells, if the latter are 
used. See another portion of these instructions for “Care of Dry Cells” 
or the instructions accompanying the storage battery, if the latter is used. 

One of the most important factors in the successful operation of a 
harmonic system of selective ringing is the keeping of the various cur¬ 
rents used at the proper frequencies. Where a motor driven set is used 
for the source of ringing current the frequency can be found at any time 

























HARMONIC PARTY LINE SYSTEMS 


461 


by a speed indicator and a watch. However, in a large number of cases 
the ringing currents are furnished by pole changers. 

Since these pole changers have no rotating part, determination of the 
frequency of the current delivered has been a task of some difficulty. 
Although the meter here described furnishes a convenient means of meas¬ 
uring the frequency of any alternating current, it was primarly designed 
to meet the need of a meter to be used with pole changers. 

The principle employed is that of counting the alternations which 
pass through an electromagnet in a given time. To this end a spring- 
driven wheel is held from rotating by a pallet mounted on an oscillating 
shaft. Fixed on this shaft is a light polarized armature, which is held by 
one or the other pole of an electromagnet through which passes the cur¬ 
rent whose frequency is to be measured. Each alternation, by reversing 
the polarity of the electromagnet, allows the force of the wheel to detach 
the armature from one pole and throw it to the other where it is held until 
the next following alternation. Connected to the escape wheel by suitable 
reducing gears are hands which move over a dial. The hands are set to 
zero, current is allowed to pass through the magnet for a given time and, 
since each alternation permits the hands to advance, the total alternations 
during the period may be read from the dial. 

The highest frequency used in telephone work is 4500 cycles per min¬ 
ute or 75 cycles per second; this requires the escapement to act very rap¬ 
idly to respond to such a current. The method of obtaining this speed 
may be explained by reference to Fig. 549. 



A prime-driven wheel W has teeth which engage with the impulse 
faces of the pallet P mounted on a rock shaft. To this shaft is attached 
a light armature A with ends similarly polarized by the permanent mag¬ 
nets N and N'. An electromagnet MM has poles MP and M' P 1 which act 
as stops to the motion of the armature and hold the armature in either 
position against the force of the wheel as transmitted through the pallet. 
For example, assuming the left-hand armature to be held by M'P', if a 
current is now sent through MM in a direction to weaken the magnetism 
of M'P', as soon as this holding force is made less than the force of the 
wheel tending to throw the armature from the magnet, the armature will 
rotate to the right, come in contact with the MP, the tooth of the wheel 
will escape the right-hand point of P and the escapement will come to 
rest with a tooth of the wheel locked on the left-hand point and tending to 
rock the shaft to the original position. However, this motion will be pre- 



































































462 


TELEPHONOLOGY 


vented by the attraction of MP for A. The next reversal will weaken the 
electromagnet, and the armature will then return to its original position. 
It is evident that for each cycle of two alternations the wheel W will be 
advanced one tooth, and by connecting hands to W by suitable reducing 
gears the number of cycles passing through MM may be read. 

This escapement is very sensitive, for all of the work of rocking the 
pallets with the attached armature is done by the force of the wheel, 
which, as before stated is driven by a spring. In practice the inventor 
states that he has had no difficulty in constructing this escapement to 
respond positively to currents of 165 cycles per second, considerably 
above the frequencies met in commercial work. If there were any reason 
for so doing it is probable that the mechanism could be made to respond 
to frequencies of 300 cycles per second, since it is only a question of the 
torque on the wheel W. In this case, however, one would perhaps have 
to use a small transformer to step the current up to about 4,000 volts to 
to use a small transformer to step the current up to about 400 volts to 
overcome the high impedance of the magnet MM at that frequency. 

The current required to run this meter is very small, on the order of 
0.005 amp; the magnet is made with a resistance of about 1,000 ohms and 
with this resistance requires for a current of 70 cycles per second a volt¬ 
age of about 80 across its terminals. For lower frequencies less voltage 
is of course required. 

From the construction of this meter it will be seen that its indica¬ 
tions are independent of the wave form of the current measured. In fact, 
since there is a condenser wired in circuit with the magnet MM it will 
respond to makes and breaks of a unidirectional current. It is not affect¬ 
ed by temperature or variations of voltage. Providing that enough cur¬ 
rent is sent through it to work it, any excess will not change its indica¬ 
tions. 



Fig. 550. H. C. Co., Portable type—Switchboard type. 


While this meter was designed primarily for work with pole chang¬ 
ers, it is very convenient for measuring the frequency of an alternating 
current of any kind. One does not have to be at the generator, as is the 
case where a speed indicator is used, but may use the meter in any place 
where the wires carrying the current are accessible. 

In addition to the Dean harmonic ringer previously described, in 







HARMONIC PARTY LINE SYSTEMS 463 

which the period of the vibrating reed is determined by means of clappers 
of different weights, several other forms of construction are offered. 

The Stromberg-Carlson harmonic ringer is shown in Figs. 551 and 
552. The weights as shown, are permanently fastened on the end of the 
armature, to the centre of which is riveted a steel reed. When assemb- 
ling each ringer, the adjustment is secured by grinding this reed, thereby 
allowing for inequalities in material or manufacture. 

The 16 cycle ringer is wound to a resistnce of 2500 ohms and the 33, 
50 and 66 cycle ringers to 500 ohms. The only difference between the 16 
and 33 cycle ringers is in the size of the armature weights, the 33 cycle 
being smaller. The reeds are also differently adjusted. 

In the 50 and 66 cycle ringers shown in Fig. 552 no armature weights 
are used the adjustment of the reed being all that is necessary. 


Fig. 551. Fig. 552. 

The design of the ringer is such that a complete disassembly of ail 
parts may be had by taking out the complete armature and the ringer 
spools. The distance of the pole pieces from the armature is adjusted by 
turning the pole pieces up and down and locking same into place by means 
of lock nuts provided for the purpose. This adjustment is made in the fac¬ 
tory and very seldom if ever need be changed by the customer except when 
the instrument is used on very long or high resistance lines. The lower end 
of the pole pieces fit into slots in the mounting plate to avoid any possible 
twisting or working loose of these parts. Fig. 553 shows the ringer dis¬ 
assembled. 












464 


TELEPHONOLOGY 


The only adjustment necessary when putting up the instrument is to 
properly adjust the gongs same as in an ordinary ringer. The gong posts 
are riveted to the mounting plate and the adjustment of the gongs is 
obtained by having them drilled slightly off centre. Loosen the lock nuts 
holding gong, and turn with the fingers until the gong is proper distance 
from the striker ball, this being determined by asking the operator to ring 
on the line with the proper current. Adjust the gong so that a loud ring 
is secured. Then ask the operator to ring on the line with the other three 
currents, in which case the clapper should not tap the gong. If it does, 
the distance between the clapper and the gong should be adjusted to allow 
the clapper to vibrate but not hit the gong except when actuated by the 
proper current. To prevent the gongs from working loose, due to the vig¬ 
orous vibration of the tapper rod, lock nuts are furnished. 

Fig. 555 shows the usual method of wiring magneto phones for har¬ 
monic ringing. The generator has a special commutator, designed to give 
a rapidly pulsating current which does not affect the ringers on the line, 
when calling central. In series with the harmonic ringer is placed a 1 M. 
F. condenser. 

It will be noticed that these instruments are wired for either 4 or 
8-party service. When using the instrument for 4-party service with a 
single wire grounded line, connect the line wire to either one of the line 
posts and the ground wire to the remaining line post and the centre post 
marked G. Then connect clips A and B consisting of the bell terminals, 
to terminals marked 1 and 2. 




On metallic lines connect the line wires to the two line posts marked 
LI and L2, and connect the centre post marked G to ground if lightning 
protection is desired,—if not, do not connect anything to G. Connect bell 
clips A and B to terminals 1 and 2. 

From the above, it will be noticed that no particular method of con¬ 
necting the instruments is followed, and the instruments need not be put 
up in rotation. That is, on a line, the fourth party ’phone can be put up 
first. Then the second, then the first or third. 

When used as eight-party instruments, it is necessary to bridge four 
bells from each side of the metallic line to ground. Talking is at all times 
metallic. In putting up an instrument, the line wires should be connected 
to the line posts, and a ground wire to G. This ground should be made 













































HARMONIC PARTY LINE SYSTEMS 


465 


in the best possible manner to insure satisfactory ringing. After observ¬ 
ing these points, ask the operator to throw the proper key for the party it 
is desired to connect the instrument up for, and it will be found that by 
connecting B clip on bell to terminal G, and then connecting A clip to ter¬ 
minal 1 or 2 that in one of these positions, the bell will ring. Of course 
the bell must be adapted to the cycle current being used. 

When through connecting the eight instruments in the manner above 
described, it will be found that four of the bells are bridged from each 
line to ground, and it will be observed that the method of connecting these 
instruments and testing out is far simpler than with any system hereto¬ 
fore offered. 

In another type of this instrument two condensers are used instead 
of one, viz., at 1 M. F. condenser in series with the ringer and i/2 M. F. 
condenser in series with the receiver, as shown on left in Fig. 554. By 
the use of the low capacity condenser in the receiver circuit, it is possible 
for one party on a line to call for another party on the same line without 
having to hang the receiver on the hook, while Central is ringing the want¬ 
ed party. While the single condenser circuit shown on the right, Fig. 555, 
accomplishes this to some extent, still better results in some instances are 
secured when two condensers are used. In exchanges where parties on 
the same line do not call for each other frequently, it is unnecessary to 
use the instrument with two condensers. 



Fig. 556. 


Any standard magneto telephone can be re-equipped for this system 
by changing the ringer and installing a condenser in the ringer circuit, 
the condensers usually being mounted on the door of the telephone. It is 
advisable to install the special generators as above re erred to, but in a 
great many instances the telephones can be very satisfactorily operated 
without any change in the generator except to remove therefrom one or 
two of the bars or magnets, thus weakening the generator current. This 
combined with the use of a low wound drop at the switchboard prevents 
the generator current from causing any of the party line bells to tap. 

The vibrating converter furnished by Holtzer-Cabot Electric Co., is 

30 











466 


TELEPHONOLOGY 



shown in Fig. 556. In operation and principle it is similar to those pre¬ 
viously described. Fig. 557 shows one of the vibrating units, and Fig. 558 
shows one method of connect¬ 
ing this converter to a master 
key. This machine is furnish¬ 
ed complete with a separate 
switch for each unit, a revers¬ 
ing switch, fuses, etc., mount¬ 
ed on a slate base in the cabi¬ 
net, which also holds the trans¬ 
formers and batteries. This 
makes a very convenient set 
and one in which trouble can 
be located or adjustments 
made without loss of time. 

Referring to Fig. 558, it 
will be noted that the 33 cycle 
vibrator is allowed to run all the time, to supply ringing current for ordi¬ 
nary bells. The 16, 50 and 66 cycle vibrators however, do not start unless 
a master key button is depressed. 



When using a master key for starting the vibrating units, care must 
be taken to allow sufficient time to elapse for the vibrators to reach their 
proper speed, before operating the cord ringing key, otherwise more than 
one bell will ring. This is particularly liable to happen with the 16 and 
33 cycle units, which take 1*4 to 2 seconds to reach their proper speed. 

As each exchange often requires a special circuit arrangement, and 
each switchboard system differs in details, no attempt will be made to 
show the varied key and circuit combinations used with this harmonic 
equipment, as sufficent has been said to show that it is capable of arrange¬ 
ment to meet any occasion in magneto or common battery work where an 
efficient selective signalling system is necessary. 


























































CHAPTER XIII. 


LINE AND CABLE CONSTRUCTION. 


One of the most essential elements in first-class telephone service is 
good outside construction. Poor construction is always getting out of 
order, and the cost of maintenance in two or three years will far more 
than exceed what good construction in the beginning would have cost. 
Poor construction not only proves a source of annoyance to the owner 
of the individual line which is poorly constructed, but it makes the entire 
service bad when this line is connected to the switchboard with others. 
In this respect a telephone exchange is not unlike the human system, as 
one broken arm or leg effects all the other members, so does one bad line 
affect all the others. 

The following brief specifications will serve as an indication of the 
usual methods of construction in common use. No attempt is made to 
completely cover the subject of line construction, as methods and ways 
are as varied and numerous as the various forms of telephone equipment, 
and differ in various parts of the country. 

Size of Poles .—Poles should be at least 25 feet long, 28 inches around 
the body 5 feet from the butt, 6 inches in diameter at the top, and rea¬ 
sonably straight. Cedar is the best timber, but chestnut is fairly good. 
In building country lines it often happens that the route of the wire 
crosses a hollow necessitating the use of a high pole. As it may be im¬ 
possible to secure one without a very great deal of expense and loss of 
time, a writer in the American Telephone Journal suggests the following 
method of splicing two or three poles together, which makes a very 
strong pole and, at the same time, is not expensive. Referring to Fig. 
559 it will be noticed that the ends to be spliced together are shaped as at 
c. They are then tightly bound with wire. At the top of the pole a bolt 
is driven through and to this four steel wires a, are attached which are 
separated by means of spreaders, as shown at c in the figure. At D is 
shown the sort of spreader to use. These wires should be brought down 
to the base of the pole and fastened in a similar manner to that employed 
at the top. When well done the pole will be as staunch as if it was made 
of a single piece of wood. On the left side of Fig. 559 is shown the use 
of three poles to secure one long one. The tension wires should be 
grounded so as to prevent injury from lightning. 

Stakinp .—The first thing to do is to stake out the line. This should 
be done with a great deal of care to get the poles in absolute alignment. 
If the line is crooked every pole will have to be guyed in order to keep the 
wires from pulling it over, and this makes the line expensive. 

( 467 .) 




468 


TELEPHONOLOGY 


Distance .—Stakes should be set 100 to 150 feet apart (depending 
upon the number of wires, etc., 160 feet is a good distance) and the 
holes dug in exact alignment. On uneven ground or in going over hills 
the poles should be set closer together than on even ground. Set two 
long stakes as far apart as they can be seen, then fill in between them. 

Poles .—Poles should be set in the ground in accordance with follow¬ 
ing table and the earth well tamped in. It is a good idea to tamp stone 
around the foot of the poles with plenty of dirt to keep the foot firm. Use 
short poles in going over hills and long poles in valleys, so that the top 
of your line will be as level as possible. 




Fig. 560. 


Table showing depth to set poles: 


Length of Pole. 

Depth in Ground. 

Depth in Solid 

Rock 

25 feet 

or 

less 

5 feet 

3 

feet 

30 “ 

a 

ii 

51/2 “ 

31/2 

ii 

35 “ 

ii 

ii 

6 

4 

ii 

40 “ 

it 

ii 

6 

4 

ii 

45 “ 

a 

ii 

61/2 “ 

41/1 

ii 

50 “ 

a 

it 

7 

41/2 

ii 

55 “ 

a 

ii 

71/2 “ 

5 

a 

60 “ 

a 

ii 

8 

5 

a 

65 “ 

a 

ii 

8 V 2 “ 

5 

a 

70 “ 

a 

it 

9 

51/2 

a 


All pole holes should be dug large enough to admit the pole without 
stabbing or hewing, and should be full size at the bottom so as to admit 
of the use of iron tampers. 

Railroads .—In crossing railroads, wires should be carried at least 
twenty-seven feet above the tracks and firmly secured to double cross 
arms with iron pins and large glass insulators. It is well to observe the 
same rule in crossing large streams. 

Framing .—Before setting the pole in the ground, the top of the pole, 
which should never be less than six inches in diameter, should be “roof¬ 
ed.” This can best be done with a hand-saw. Five or six inches from 
the peak of the roof the first ?ain should be cut. The standard gain is 
one inch deep by 4% inches wide, but gains may be proper size to admit 






































LINE AND CABLE CONSTRUCTION 


469 


the cross-arm. It is also well to cut other gains 18 inches below each 
other, in order to admit more cross-arms should more wires be required 
than can be carried on one cross-arm. See top of pole, Fig. 560. 

Brackets. —If brackets are used instead of cross-arms, the first 
bracket should be placed so the top will be level with the top of pole; and 
if two wires are used, the second bracket is placed eighteen inches below 
the first, on the opposite side of the pole, except on curves and corners, 
here both brackets must be on the outside of the curve. Use one sixty- 
penny and one twenty-penny nail to secure each bracket. 



Fig. 561. 


Cross Arms. —Before raising a pole a cross arm should be bolted to 
the top gain with two one-half inch bolts with washers beneath head and 
burr, the dimensions of a 10-pin cross arm are given in Fig. 561. Two 
iron braces 20 inches long should be bolted on the cross-arm with S 1 /* 
inch carriage bolts and secured to the pole with a 3 inch lag bolt. The 
pole is now ready to raise. Care should be taken in framing the pole to 
cut the gains opposite belly of the pole or in such a way that when the 
pole is set the straight side of the pole will come into alignment. This 
gives the line the apppearance of good workmanship. On straight lines, 
the cross-arms should be put on alternating sides of the pole as shown in 
Fig. 562. 





Fig. 562. 



Guying. —Before stringing any wires all poles not in perfect align¬ 
ment must be thoroughly guyed, the guy line having a strength ten times 
as great as the ordinary strain on the line, See Figs. 563-564. Then the 
strain of the wires is on the pole instead of the bolts. The reason for 
this is the danger of sleet storms and the natural increase of wires on the 
line. In turning corners the poles must be guyed as shown. 

Anchors. —Where there is no tree or other substantial anchorage it 
is necessary to set a strong post in the ground or bury a dead man, as 
shown in Fig. 565. This latter consists of a log or large stone buried 
fully five feet deep, to which the guy is attached. The best method is to 
use an anchor of the type shown in Fitr. 565. The anchor is driven into 
the ground the desired depth with a sledge or maul. The blades are set 
by twisting to the right three revolutions. The design of the blades, like 
those of a screw propeller, causes them to spread when the anchor is 





























470 


TELEPHONOLOGY 


twisted. The pitch is such that they spread to an angle of ninety degrees 
with the rod in three revolutions. The spread of the blades sinks the 
anchor about one inch, so that there is absolutely no lost motion in the 
ground. The pull is on solid earth that has not been disturbed. The 




Fig. 564. 


anchor can be set by one man in sixty seconds. Heavy poles should be 
selected for corners, as they have a much greater strain than the others: 
it is a good idea on corner poles to place a cross-arm on both sides of the 
pole, bolt through same outside to outside, with a block between the ends 
also bolted together. 



Fig. 565. 



Distributing Poles .—Where only two wires are required such, for 
instance, as connecting a house with the main line, smaller poles may be 
used and brackets used instead of cross-arms, as shown in Fig. 566a. 

Tieing .—If the line is not straight, observe method of tieing wires 
to pins shown in Fig. 566, right hand side. 

Bracing .—At the end of each line of wire or in going over a steep 
hill, the line should be thoroughly braced for two or three poles, as shown 
in Fig. 567. This takes the strain off the end pole, which otherwise would 
be apt to break off in a sleet storm, letting the strain come on the next 
pole, which is also quite sure to break, and in this manner ruin the entire 
line. 

Making Guys .—Guys are made of a number of strands of wire twist¬ 
ed together. Each guy is generally different in some respects from the 
others, but a little judgment will show the general requirements. For a 



















LINE AND CABLE CONSTRUCTION 


471 


six-wire line, twist three wires into a strand and anchor to a tree near 
the ground, or as shown in Figs. 568-569. A 12-wire line will require a 
5-strand guy. Remember that in building a line this is the most impor¬ 
tant part of the work and the part generally neglected. The breaking of 



Fig. 566. 


a guy wire may not only break the pole, but it will let the entire line sag 
and the wires swinging together will “short-circuit” and cause constant 
interruptions to the service. Guy wire can be purchased far cheaper 



than it can be made, but in case of necessity, a good way to make a guy 
is to cut off the number of wires required all the same length. Fasten 
one end of the strands to the spokes of a wagon wheel and the other end 
to some distant object. Raise the axle to free the wheel from the ground 
and turn until the strands are sufficiently twisted. Only B. B. or soft 




wire No. 14 gauge, can be used in this manner. Fasten the guy around 
pole with clamps as shown in Fig. 570. 

Stringing Wires.— When the pole line is thoroughly built and guyed, 
the wires can be strung. This should be done collectively. That is, if 
there are six wires to string, do them all at once, drawing from six reels 
at the same time. 









































472 


TELEPHONOLOGY 


MESSENGER WIRES AND GUY WIRE. 


7 Wires 

Approximate 

Weight 

Tensile Strength 

No. 

Diam. Inches. 

100 feet. 

Pounds. 

8 

1-2 

52 

8320 

9 

15-32 

42 

6720 

10 

7-16 

36 

5720 

11 

3-8 

28 

4640 

12 

5-16 

21 

3360 

13 

9-32 

16 

2560 

14 

17-64 

12 

1920 

15 

1-4 

10 

1600 

16 

7-32 

8 

1280 

17 

3-16 

6 

960 

18 

11-64 

4 3-10 

688 

19 

9-64 

3 3-10 

528 

20 

1-8 

2 4-10 

384 

21 

3-32 

2 

320 


Fig. 570. Fig. 571. 

Reels .—A wire reel is shown in Fig. 571. Make or purchase as 
many reels as needed. To make a reel take two pieces of 2x4 scantling, 
two feet long, halve them together and nail solidly in the form of an X. 
Fasten a 4x4 block on the center by spiking at the corners. Bore a 1 
inch hole in the center, and insert a pin 12 inches long, which will pro¬ 
trude 8 inches. Now halve two more pieces together, nail solidly and 
bore holes in the centre so as to turn easily on the standard. In the arms 
of this second piece bore a number of inch holes to allow of adjusting to 
the size of the coil of wire to be used. Four pins will hold the coil on the 
reel and allow it to unwind. 

When a reel is provided for each coil, set them in a row and attach 
the end of a wire from each coil to a 2x4 scantling or stick 2 feet long, 
the wires being about evenly distributed from one end to the other. Now 
tie the ends of a ten foot rope to the ends of the stick and a long rope in 
the center of the short rope so it will pull in the form of the letter Y. 
Throw the long rope over several cross-arms near the poles and hitch a 
horse to the other end. As the horse passes the poles, let the workmen 
continue to throw the rope over additional cross-arms until the horse can 
draw it no further. Fasten the wires to the cross-arms temporarily, 
bring forward the reels and proceed again as before. 

Drawing Up .—When the wire is drawn, first make sure that the 
head pole, or the end of the line is properly guyed to prevent it from 


















LINE AND CABLE CONSTRUCTION 


473 


being pulled over, screw the glass insulators on the pins, tie the ends of 
the wires thoroughly by winding them twice around the glass knob and 
twisting the end around the body of the wire, as shown in Fig. 572. Then 
go to the other end of the line, draw one of the centre wires and fasten 
it to the body of the next pole near the ground. Then take the next centre 
wire in the same manner, continuing until all the wires have been drawn 
and fastened to the body of the pole, observing to draw each wire with 
an equal tension, and tie the same as above described, except that instead 
of bracing the head pole, unfasten four of the wires from the body of the 
pole (leaving two wires for the time as a temporary guy), and splice 
them upon the new lead, then proceed as before. 

In passing through trees, never fasten the wire to the tree direct, 
for the swaying of the tree will either break the wire or pull something 
loose. Always fasten as shown in Fig. 573. 



Fig. 572. 


Fig. 573. 


In building lines through timber country the ordinary ladder is often 
of not much use on account of the limbs of trees interfering with the 
position it would occupy. To overcome this difficulty, a writer in the 
“Journal” designed the rope ladder which is illustrated in Fig. 574. The 
design is such that makes it easily carried, and yet of sufficient length 
to allow reaching the lowest branch of a tree, about 18 or 20 feet. The 
ladder is supported to the branch by means of a hook fastened to a bow¬ 
shaped piece of iron, which holds the side ropes. The rod shown to the 
left of the ladder is composed of pieces of pipe held by thumbscrews, and 
is used to hook the ladder over the branches. 



Fig. 574. 


























474 


TELEPHONOLOGY 


Sagging Wires .—In putting up a lead of wires, be very careful to 
draw them all to about the same tension, the amount of sag being given 
in the acccompanying table. 


The following shows sag for No. 8 and 12 wire. For No. 14 allow 
about 2 inches more for same temperature and span: 


Temp. 


Length of Span In Feet. 



Degrees 

75 

100 

115 

130 

150 

200 

Fahr. 


Sag In 

Inches. 




30 

1 

2 

21/2 

31/2 

41/2 

8 

10 

H / 2 

21/2 

3 

4 

5 

9 

10 

IV 2 

3 

31/2 

41/2 

6 

101/2 

30 

2 

3 

4 

51/2 

7 

12 

60 

2 i / 2 

41/2 

51/2 

7 

9 

151/2 

80 

3 

51/2 

7 

81/2 

IH /2 

19 

100 

41/2 

7 

9 

11 

14 

221/2 



Tieing and Splicing .—To make a tie take a piece of wire same size 
as that used for the line wire and wrap same around insulator, as shown 
in Fig. 575, then wrap tie around the line wire, NOT in a close spiral but 
with the turns slightly apart as indicated. This prevents water from 
lying between the turns and thereby rusting the tie. Do not strain the 
service. A good splice welll made does not require any soldering, and it 
tie wire around the insulator, as the expansion and contraction of the 
line wire and glass is not the same the glass will be factured. In turning 
a corner the line wire should be placed on the outside of the glass, as 
shown at “A”. Do not turn a corner as shown at “B” as in this case the 
strain is always away from the pin, and the wire will soon pull out. At 
“C” is shown the proper method of making a plice. Never nick or twist 
the wire to such an extent that the galvanizing is damaged. The wire 
should be wrapped tightly or should not be marred or bruised. At “D” 
and “E” are shown some bad splices, which will cause noise and poor 
is not good practice to solder iron line wire except where a copper wire 
joins the iron line. When this is the case the joint may be soldered. 
When soldering a joint on iron wire, do not apply acid or other flux 















LINE AND CABLE CONSTRUCTION 


475 


until a moment before the solder is applied, for if the acid is applied some 
time in advance the acid will discolor the galvanizing and after the joint 
is made the bare wire will be exposed for an inch or so on each side of 
the joint which will soon rust out. 

Another point to be remembered is that you cannot do anything 
without a good hot flame and as stated before, it is best to make the 
joint so that no soldering is necesssary. For long trunk lines use No. 8 
or No. 10. For long heavily loaded country lines, No. 12. For short 
town lines, No. 14 may be used. While the EXTRA B. B. is best from an 
electrical standpoint, for all ordinary purposes, use the B. B. grade. The 
steel wire will give satisfactory service when the lines are not too long. 
When very long spans are used such as crossing a river, it is well to use 
a steel wire on account of its increased strength. 

The following table gives the weight in pounds per mile together 
with the breaking strain and resistance of iron telephone wire: 


Weight in Approx, breaking strain Av’ge resistc’ in ohms. 



Diameter 

pounds 

Put 

up in 


in pounds 

at 68 

degrees 

F. 

No. 

in inches 

per mile 

bundles of 

E. B. B. 

B. B. 

Steel. 

E. B. B. 

B. B. 

Steel 

6 

.192 

540 

1-3 

mile 

1,620 

1,782 

1.998 

8.70 

10.19 

12.04 

8 

.162 

.,.380 

1-2 

(4 

1,140 

1,254 

1,406 

12.38 

14.47 

17.10 

9 

.148 

320 

1-2 

44 

960 

1.065 

1.184 

14.69 

17.19 

20.31 

10 

.135 

260 

1-2 

44 

780 

858 

962 

18.08 

21.15 

25.00 

11 

.120 

214 

1-2 

44 

642 

706 

792 

21.96 

25.70 

30.37 

12 

.105 

165 

1-2 

44 

495 

545 

611 

28.48 

33.33 

39.39 

14 

.080 

96 

1-2 

44 

288 

317 

355 

48.96 

57.29 

67.71 


Noisy Lines and Their Cure. —When two lines are strung for any 
distance parallel to each other and current is flowing in either, there is a 
current induced in the opposite direction in the other, the result of this 
induced current is cross talk and in the case of grounded lines, there is 
no way to overcome the trouble. 

One grounded line and any number of metallic circuits may be 
strung on the same pole for any distance without having cross talk, if the 
metallic lines are transposed. 



In Fig. 576 is shown the effect of having one or more grounded lines 
on the same poles and cross arms. It will be noticed that as indicated by 
the arrows, the current in one line is in an opposite direction from that 
induced in the other. 

It will at once be seen that if the wire “A”, which we will take to be 
the disturbing wire, is an electric light or other wire carrying a heavy 











476 


TELEPHONOLOGY 


current, that the induced currents in the line “B” will be of such a nature 
as to seriously interfere with the satisfactory operation of the telephones 
which are represented by the receivers “T” and “D”. Or if the wire A 
is a telephone wire, the noise induced in “B” will be of the variety com¬ 
monly known as “cross talk.” 

Transposing will be found to cure this trouble if the lines are made 
metallic. This is shown in Fig. 577. Here it will be seen that the cur¬ 
rent'in the metallic line is in an opposite direction to that of the disturb¬ 
ing wire “A” and since the transposition of the metallic line causes the 
induced current to flow in first one direction and then another, these cur¬ 
rents will neutralize each other, and as the transpositions are cut at equal 
distances apart, the pressure of the currents are the same and therefore 
no current will flow through the receivers at each end of the line and the 
line will be unaffected by outside influences as long as the balance of the 
line itself is maintained. 




In cases where there are more than one metallic line on the same 
poles, all of them must be transposed but not at the same place, as in this 
case there would be no difference in the relative position, and the effect 
would be the same as though they had not been transposed at all. There 
are several systems of transposition, but they are all only slightly differ¬ 
ent roads to the same end, and the diagram as shown in Fig. 578 is the 
method most frequently used and is ’perhaps the best. The horizontal 
lines represent the metallic circuits and the poles shown represent every 
tenth pole beginning with the pole nearest the office and counting it as 
No. 1, next No. 2, and so on. Begin with the tenth pole in the following 
order: A. B. C. B. A. B. C. B. keeping this system up all the way to the 
other end of the line disregarding any branches that may tap the line, 
and when the marking is done, the transposing is to be done as indicated. 
It will be seen that each line is transposed at either just one-half or twice 
the distance of the next circuit to it. 

It is necesssary to use what is known as transposition insulators 
when doing this work. These are the same as the ordinary insulator 
except that they have two grooves for the wire instead of one and are 
shown in Fig. 579. The method of crossing over or transposing the wire 
is clearly shown in small sketch of lower corner of diagram. This work 
should be carefully done and will be found to cure immediately the very 
common and annoying trouble known as “cross talk.” It will also cure 
inductive noises caused by lines paralleling power or telegraph wires. 

We will suppose that the metallic trunk lines in an exchange have 
been carefully transposed, and that all the local lines are grounded, or 













LINE AND CABLE CONSTRUCTION 


477 


vice versa. As soon as one of the ground lines is connected to the metallic 
line through a cord circuit in the switchboard, an unbalance results, 
which immediately makes both the metallic and grounded lines noisy, 
although either one of them by itself is perfectly quiet. This immediately 
renders useless all the transpositions which have been so carefully made, 
and some method of maintaining an equal balance between lines must be 
devised. This is accomplished by using a repeating coil which is described 
in connection with swtchboard equipment. 



TO TRANSPOSITION OF METALLIC LINES 


•» *W Am 4m '»/ Max M M TWt ftr ADA M w **• 

'•/ Mar/ A! mm mt Mm* fmrrmaet t,~t t emym/er se ■"<»/ 
Mil/ AymtAAl /><•• /* Cm*It 4«« rA./ a./ Mr mmmm 


Fig. 578. Fig. 579. 

If the line is for the purpose of connecting several ’phones together, 
connect the instruments to the outside line or lines as shown in Fig. 580 
using twisted rubber covered and braided wire to connect from the main 
line to each phone when the lines are metallic and single rubber or plain 
weatherproof covered wire when single wire or grounded lines are used. 

If it is desired to bring the bare line wires directly to the building, 
use brackets or knobs and leave sufficient slack between the last pole and 
the house to prevent the humming sound present when the wires are 
tightly drawn. 

*“When running wires to a building in a conspicuous place, it is 
desirable that they present a neater appearance than the ordinary method 
of nailing on wooden brackets can give. Iron brackets can be bought 
from the supply companies, but their cost may be prohibitive, or possibly 
there are none on hand. Following the idea here presented almost any 
type of an iron fixture can be quickly and cheaply made.” 

“A piece of strap iron is bent into the desired shape, as shown in 
Fig. 581, screw holes drilled, and its end placed in an insulator. Around 




*American Telephone Journal. 







































































































































478 


TELEPHONOLOGY 


the iron, Plaster of Paris is poured, mixed with water to the consistency 
of cream. When the plaster sets the fixture is ready for use.” 

“The type shown is only one of the many which may be made. By 
cutting in half at the middle screw hole a single bracket would be formed. 
By properly bending the strap iron a double bracket with its two insula¬ 
tors in a horizontal line could be shaped. Special fixtures to be placed on 
building corners or bolted to steel work can easily be arranged.” 



Fig. 581. 


“Strap iron is best used if a forge is not available, as it can be bent 
while cold by using a vise and hammer. The screw holes may be drilled 
with a breast drill. Any size of strap iron that will enter the hole in the 
insulator will do, provided it is stiff enough. Judgment must be exer¬ 
cised, as in no two cases will the strain on the brackets be the same. 
Round iron is better than strap, as it is stiffer, but for most sizes it would 
be necessary to heat it before bending. If round iron is used it should 
be flattened at the points where the screw holes are drilled. This may be 
done with a hammer when hot. The whole length of iron below the first 
screw hole may be flattened so that the fixture will lie closely to its sup¬ 
port.” 

“Screw holes are best placed directly in the line along which the 
strain is to be. If this is done there will be no bending action at the point 
where the screw hole is drilled, where the iron is weakest. This is illus¬ 
trated in figure. The bottom screw hole being placed directly back of the 
groove in the insulator, thus, when a strain is brought on the insulator, 
there will be a tendency to pull the screw from the wood, but there will 
























































LINE AND CABLE CONSTRUCTION 


479 


be no tendency to bend. In the bracket shown it would be impossible 
without altering its construction, to so place the upper screw hole that it 
would fulfill the above conditions.” 

“When a screw comes directly behind an insulator some trouble may 
be experienced in turning it into place, the insulator being in the way of 
the screw driver. This can be avoided by first turning the screws into 
the wood as far as they will be required to go, before the bracket is in 
place, using it as a templet to determine their positions. The screws can 
now be removed, the brackets replaced, the screws reinserted and turned 
until tight.” 

The inside wiring is greatly neglected especially by those doing the 
work in small exchanges. There are many reasons why inside wiring 
should be properly done. Aside from the question of good looks, the 
inside wires should be properly installed, so that the trouble resulting 
from loose and broken wires is eliminated to as great an extent as pos¬ 
sible. 

Where the outside lines run for any distance, it is necessary to have 
a lightning arrester, a standard form of which is shown in Fig. 130, 
page 98 this being of the choke coil variety. A standard carbon and fuse 
arrester is shown in Fig. 582, this being installed as a unit, where the 
lines enter the building, or where the ground connection is nearer the 
instrument than the line entrance, the fuses may be mounted on a sepa¬ 
rate block, shown in Fig. 583, while the carbon arrester is mounted sepa¬ 
rately as shown in Fig. 584. 



Fig. 582. Fig. 588. Fig. 589. 


After deciding where it is necessary to bring the outside lines into 
the building, suitable holes should be bored, and porcelain tubes should be 
placed in the holes. It is supposed that the wire entering the building is 
of the twisted pair, rubber covered variety, and is joined to the bare wire 
lines at the first pole nearest the house. In this case the twisted pair 
comes through one tube into the house, and is connected directly to the 
lightning arrester, which should be placed as close as possible to the 
point where the wire enters. This is shown in Fig. 580. 

The line wire should connect directly to the post of the lightning- 
arrester. Where the wires enter the proclain tube a short loop should 
be made on the outside to keep rain from running in on the wire. 

The next operation is to connect the ground wire to the lightning 
arrester. The ground wire should be suppported by small porcelain 
knobs like those shown in Fig. 580, which also shows how the ground 
wire is tied to the knob. The wire should be fastened to the knob as 


4S0 


TELEPHONOLOGY 


shown, great care being taken not to make any sharp bends, twists or 
curls; the wire should be as short and straight as possible. Use No. 14. 
Methods of making the ground connection, ground clamps, running the 
ground wire etc., are described on pages 100 to 101. 

In case no lightning arrester is used except the one usually furnish¬ 
ed on the telephone instrument, the ground wire should connect to the 
ground post on telephone, usually the centre one. 

After fastening the telephone in place upon the wall, the line wire 
can be run from the arrester to the telephone. The best wire for this 
purpose is rubber covered and braided twin wire. This can be secured at 
a slight additional cost over the ordinary annunciator wire sometimes 
used, which is not at all satisfactory for this purpose. 

The wire can be held in place by small wooden cleats, porcelain knobs 
or insulated staples. In .using staples or tacks, it should always be borne 
in mind that only one wire should be brought under the staple; never 
put both wires under the same tack as trouble will result. The wire 
should be tightly stretched so as to make a neat job. In a great many 
cases the wire can be run back of picture moulding or around the edges 
of window frames, and thus kept out of view. 

The line wires entering the telephone and lightning arrester posts 
can be curled into small spirals. Do not treat the ground wire in this 
manner however. The ends of the wire should then be carefully bared, 
doubled back and formed up into a tip so that the wire will not be cut off, 
if screw binding posts are used. This lends strength to the wire, and 
prevents the screws cutting it off when the wire is placed in the hole on 
the binding post. All connections should be tight. If not, a rattling, 
scraping noise will occur. 

Particular attention should be paid to suitably locating the tele¬ 
phone. It is very bad practice to mount a telephone on a damp wall or in 
any place where it is liable to be damaged in any way. Telephones should 
not be located on lathed or plastered partitions of buildings, as such a 
location will cause a ringing sound in the telephone if there is much noise 
around. When putting a telephone instrument on a solid brick wall, it is 
well to hold the telephone in position and mark the screw holes by driving 
a nail through them. Then remove the telephone and drill the holes by 
means of a chisel. Wooden plugs can then be driven into the holes, and 
the telephone held in place securely by screws inserted through the plugs. 
In any event the instrument should be solidly mounted. 

With some types of telephones, the batteries are located in a closet, 
or some other suitable place. In this case it will be apparent that the 
wires connecting the telephone with the batteries should not be long 
enough to offer any serious resistance, and if the batteries used are of the 
wet cell type, great care should be taken to place them where they will 
not freeze or become over-heated. This is especially the case when bat¬ 
teries are placed in cellars, as they are often put on shelves near heater 
pipes, which soon renders the batteries worthless. 

When a switchboard is to be connected up it is best to end all the 
wires of the exchange on a pole directly outside of the exchange building. 
A suitable cable box can be located on the pole and a weather-proof 
cable connected from the cable box directly to the lightning arrester 
distributing frame or other device in the “Central Office” to which the 
cable from the switchboard is connected. Fig. 585 represents a cable 


LINE AND CABLE CONSTRUCTION 


481 


box of the usual pattern. This should be firmly attached to the pole by 
two sh ° rt cros s-arms and bolting them fast to the pole. The 
able box can then be attached to the cross-arms by means of lag screws. 

ine- thf^lirTPQ 6 a °,f sbouk | located slightly below the cross-arms carry- 

cable^box*Vw Smal dGCk v° r platform should be erected below the 
cable box so that the work can be conveniently done in the box. 

carbons P? vlded inside with strips of terminals, fuses, or 

to thesn fprmln V nd K P ates ’ and the P airs of wires should be connected 
mind tW fih l a] . s , h J me ans of twisted weather-proof wires. Bear in 

as is h ptnn« Pairased for inside work cannot be used on a pole 

talk anH 1S! d p J?k we . ath f aad whe n it becomes wet will cause cross 

nrnrn!nl^ k . R H bb !F ™u\nted or braided weather-proof wire is rec¬ 
ommended for wiring the poles. 



Fig. 585. 


The following method of connecting up a small exchange will be 
found of interest: 

Metallic Lines. —Carefully solder a twisted pair of wires to each line, 
then run the twisted pair through insulated iron or leather rings placed 
on the pole at convenient intervals until the wire reaches the cable box. 
Then connect it to a pair of terminals in the box, as shown on the right 
hand side of Fig. 586. 

“ Grounded” or Single Wire Lines. —One single weather-proof wire 
should be soldered to each line wire. This should run through the rings 
and join the top terminal of each pair in the cable box, as shown on the 
left hand side of Fig. 586, which also shows that the bottom terminal of 
each pair in the cable coming from switchboard, is securely connected to 
the ground in the cable box as shown in Fig. 586 by the strap wire X. It 
will be observed from the above that the exchange will always be wired 
full metallic completely from the switchboard to the cable box, and that 
when grounded or single line wires are used, one side of the metallic pair 
coming out from the switchboard will go to the ground in the cable box. 
This method of grounding in the cable box will prevent a great deal of 
cross talk. While more wires from switchboard to cable box are neces¬ 
sary when using this method, greater satisfaction is gained as it is not 
good practice to run the single lines into the switchboard and then con- 
31 













482 


TELEPHONOLOGY 


nect one side of the switchboard jacks together and run same to the 
ground, as this brings all the grounded lines in close proximity to each 
other where they pass through cable from the terminal pole to the switch¬ 
board which causes a great deal of cross talk. 

Where the number of lines exceed five, it is best to use weather¬ 
proof cable to connect from the box on pole to Central Office lightning 
arrester; rubber insulated weather-proof cable is made up of twisted 
pairs of wires. Each twisted pair should be connected to a pair of line 
terminals in the cable box. This end of the cable should be formed up for 
connecting to terminals in cable box, as shown in Fig. 586. 

Take a board as shown in Fig. 587, of proper size and drive nails in 
it at points corresponding to terminals on lightning arrester, fan out 
and lace up the cable wires by means of twine so that each pair of wires 
is in a proper position to reach the terminals in cable box without having 
a great tangle of wires in the box. In the figure C C C shows the nails, 
spaced same as the terminals in box. The distance A is the length that 
should be allowed so that wires will join terminals without having too 
much slack. Line S shows where wires should be skinned. 



The four upper figures show method of forming a “but,” or end for 
the outer braiding of the cable. 

Figs. 588 and 589 show how to open and lace the cable. The cable 
should be supported by means of a leather strap wrapped around the 
cable and fastened to the pole. The other end of cable should be opened 
up and formed out in the same manner. It will be necessary in this case 
to test out each set of wires to find out how the wires should be distrib¬ 
uted. This can be accomplished with a bell and two batteries, as shown in 
Fig. 590. 

From this it will be seen that the end of the cable which connects in 
the cable box can be distributed without any regard to testing out each 
pair of wires, but that the end going into the lightning arrester in the 
office should be tested out and the pairs numbered 0, 1, 2, 3 and 4, etc., to 
correspond with the end in the cable box as shown in Fig. 590. The wire 
from the battery is first connected to one wire in the cable and then the 
wire connected to the bell is touched to the bared ends of each one of the 
wires on the other end of the cable until the bell rings. This will denote 
the correct pair and it can be distributed as described. 























483 


LINE AND CABLE CONSTRUCTION 


The office end of the cable should be connected to the carbon and fuse 
lightning arrester so that the circuit passes through the fuses first, and 
then to the carbon side of the arrester, and to the switchboard. 

Another, and perhaps the most vital point to be observed in connect¬ 
ing up this cable, is the following, which is particularly important when 
grounded or single wire lines are used: 




Fig. 587. 


Fig. 589. 


Fig. 588. 




"«0 MMKATlOrt 
wit* * D<X''t T . 


O* or 


The wires in the weather-proof cable which connect with the lower 
terminal of each pair in the pole box and which in the case of ground or 
single wire lines are connected to the ground strip, are run into the 
lightning arrester and connected to the lower carbon and fuse of each 



pair. A diagram of this condition is illustrated in Fig. 591 which shows 
a pair of wires extending from the carbon and fuse lightening arrester 
out of the cable box strip, one o p them being connected to the ground in 
cable box and the other continuing out as a single wire or grounded line. 



In case of metallic lines, this point is not of such vital importance, 
but in the case of grounded lines, it is vitally important that all the bot- 






































TELEPHONOLOGY 


484 

tom terminals of each pair on the lightening arrester should be connected 
to the wire in cable which connects to the ground in the cable box. 

Fig. 592 shows the next operation which consists of connecting the 
lightening arrester to the switchboard cable. It will be seen that the 
switchboard cable terminates in a board or panel which is provided With 
terminal clips. This board is known as a “Route Board,” “Distributing 
Board,” “Distributing Rack,” and various other names, and in the case ot 
small exchanges it is always the board which is attached to the end of the 
cable coming out o fthe switchboard. This board is fastened to the oppo¬ 
site side of the lightening arrester frame from the strips of carbons and 
fuses, and each set of terminals on the board should be connected to a pair 
of lightning arrester terminals comprising a line, by means of ^a short 
piece of twisted pair wire, commonly known as “jumper wire,” which 
consists of different colored wires twisted together to form a pair. 



The bottom terminal of each pair on the lightning arrester should 
be connected to the bottom terminal of each pair on cable board. This 
can easily be done by connecting a certain colored wire of each pair to the 
bottom terminal on lightning arrester and connecting the same wire to 
the bottom terminal on each pair on the switchboard. The resulting cir¬ 
cuit is as shown in Fig. 592. 

It will now be seen that all the tips or short springs of the jacks are 
connected to the line wires in the case of ground or single wire lines, and 
that all the sleeve springs of the jacks or the long springs which make 
contact with the sleeves of the plugs when same are inserted in the jacks, 
are connected to the wires which go to the ground in the cable box. 

The reason for so much caution in keeping this circuit straight will 
readily be noted by reference to page 137 and reading the matter relating 
to reversed lines. 

The metal frame of the office lightning arrester, and the ground 
strip in the cable box should be connected to the ground. It is only neces¬ 
sary when installing a Central office to have one good ground. It is not 
necessary to have a separate ground wire for each line. The reason for 
grounding the metal frame of the lightning arrester is to provide a path 
for the ready escape of the lightning. 

The arrester equipment so far described is suitable protection 
against lightning currents, or heavy currents of considerable quantity. 
It is also necessary to protect the switchboard from so called “sneak” 
currents, which are currents of such small quantity that they will not 
operate the V2 or 1 ampere fuse commonly used, but will heat and destroy 


























LINE AND CABLE CONSTRUCTION 


485 


any ringer or drop coil that may be in the circuit. Many devices for this 
purpose have been offered, nearly all of them depending upon the heating 
effect of the sneak current on a small coil of wire commonly known as a 
“heat coil” to open the line. 

Typical of the highest development of this class of apparatus, is the 
Cook protector. These are arranged in banks of 20 or more pairs, and 
are adapted for mounting on the regular iron frame furnished by Frank 
B. Cook. The No. 10 protector is shown in Fig. 593, the banks of pro¬ 
tectors being mounted vertically, as shown in cut of complete frame, Fig. 
594. 



Fig. 593. 



Fig. 594. 


The circuit and operation of the device will be understood by refer¬ 
ence to Fig. 595, which shows one pair of protector springs arid heat coils, 
one for each wire. The top of the figure shows the coil in circuit in the 
normal condition, while at the bottom is shown a coil operated. Refer- 



















486 


TELEPHONOLOGY 


ring to the figure the line wires connect to A and A 1 . Considering the sneak 
current as entering over line A, it would pass to spring B via the contact 
between A and B and then pass through heat coil C to spring D. If the 
voltage was sufficiently great, as is the case with lightning, a path is pro¬ 
vided to ground via carbon block F, which is connected to spring D, and 
which is separated from ground carbon G by a thin piece of mica or cellu¬ 
loid. In the event that the current does not jump this gap, but continues 
to flow through D to E and through the instrument and out over the other 
side of the protector, the heat coil immediately becomes warm, the solder 
holding B to C melts, and B is released, thereby opening the circuit and 
stopping the current flow. 



Fig. 595. Fig. 597. 


When B is released, it carries with it the hard rubber strip H which 
pulls spring E against the alarm contact II 1 , thus causing a bell connect¬ 
ed in this circuit to ring, thereby notifying the wire chief of an open line. 
Only the ends of the alarm wires I, I 1 , can be seen in the illustration, but 
these run vertically through all the banks of protectors in each section of 
the frame. 

Cook’s No. 10 Protector is a re-soldering but not a self-soldering pro¬ 
tector. The protective apparatus is automatically reset by the use of a 
resetting plug, which is shown in Fig. 596. This plug closes a battery 
circuit through the heat coil. The battery current heats the coil and melts 
the solder. The plug presses the operating spring back against the heat 
coil, holding it there until it re-solders in position to operate again. The 
battery current is then automatically cut off, allowing the coil and the 
solder to cool. The plug holds the operating spring to its position in the 
coil until the solder has hardened. As soon as the plug is inserted the 
line is put in operative condition, the plug in no wise inter ering with the 
subscriber’s use of the line. The dotted lines, Fig. 596 show the spring of 
the resetting plug engaging the spring on protector. It requires about 1 
ampere to operate the plug. 

One of the novel points about the protector is that in resetting a coil 
which has operated, a test of the protector is made. Should the coil be 
defective, the operation of resetting indicates automatically that the coil 
is imperfect and it simply cannot be reset. If a self-soldering protector 
is not carefully tested after each operation, it might contain a defective 
coil which could cause a great deal of damage. This is impossible with 
Cook’s No. 10, as a heating current is closed through the heat coil after it 









































LINE AND CABLE CONSTRUCTION 


487 


ODGratfvP C °u a .? d automaticall y restore the protector to 

operative condition. Ihis reheating current tests the coil. 

Cooks No. 10 has no loose contacts (or pressure contacts) at the 
neat coils the heat coils are screwed to their mounting springs (and 
ma> be soldered as an additional precaution), and the operating springs 

are soldered to the other end of the heat coils when the apparatus is set 
for operation. 


When the protector operates, it grounds the line circuit and closes an 
alarm circuit. This automatic alarm is reliable. 

The coil itself (Fig. 597), consists of a metal casing or shell, in 
which is enclosed a graphite composition, insulated from the metal cas¬ 
ing, except on one end. The coil is so constructed that the heat is confined 
to one end, where it is utilized to soften the solder, allowing the apparatus 
to operate. The graphite takes the place of the wire in a wound coil, pro¬ 
viding the heating element in this protector. 




Fig. 596. 


Each pair of protectors is separated from the adjacent pairs by hard 
rubber strips which extend through the ground plate. These strips keep 
all the springs in alignment and provide a very substantial and durable 
construction. Adjacent pairs of springs absolutely cannot be forced into 
contact with each other. 

The No. 10 is so designed that by the use of a test plug (Fig. 598), 
it is possible to test every circuit or combination by simply inserting the 
plug. 

The springs are all mounted on a plate of formed sheet metal, which 
is unusually strong and so light that it greatly reduces the weight on the 
frame and mounting bar. 

The No. 10 protector is equipped with the improved form of carbon 
arresters, using either perforated or U shaped celluloid dielectrics .005 
o ' an inch thick. In the perforated celluloid dielectric the perforations 
are so small and so numerous, that the discharge is greatly broken up, and 
is forced to pass through the arrester at many points. This prevents par¬ 
ticles of carbon from breaking off and short circuiting the arrester. The 
celluloids do not vary in thickness, and are consequently uniform and 
reliable in their operation. If an arc continues through the arrester, due 













































488 


TELEPHONOLOGY 


to a cross with a high voltage circuit, the celluloid will melt and allow the 
springs to press the carbon blocks together and form a dead ground 
through the arrester. This stops the arc, after which, if the circuit 
increases sufficiently, the fuses at the outer end of the line will blow and 
entirely cut out the switchboard from the circuit. The exposed surface of 
one carbon is insulated with an enamel which prevents a short circuit 
from occurring at the exterior surface of the arrester. 

A combined distributing and protector frame consists of an angle 
iron frame built in vertical sections of 100 to 200 pairs. New vertical 
frame sections can be added at any time. The protectors can be readily 
attached to the frame as needed. 


TO TESTING INST" 




TEST PLUG 


Switch closed through contacts 
I & 2 tests switchboard 
3 & 4 tests line through heat coils 



5 & 6 tests line direct 
7 & 8 tests one heat coil 
9 & 10 tests other heal coil 

Fig. 598. 



The uprights are of angle iron and are securely bolted to an angle 
iron base, making a rigid and substantial frame work. To the uprights 
are secured horizontal bars of channel iron, extending from front to back. 
To the front ends of these bars are fastened vertical mounting bas to 
which the protectors are secured. 

Directly back of the protectors are mounted maple fanning strips 
extending the full length of the rack. Each strip is drilled and numbered 
to correspond to the protector pairs directly in front of it. 

At the back end of the horizontal bars, directly opposite the protec¬ 
tors, are the cable terminal blocks, mounted vertically in strips of twenty 
or twenty-five pairs each. 

For distributing the cross-connecting wires, a small insulated ring is 
placed directly back of each cable block and larger ones are secured to the 
vertical angle irons. 

A set of horizontal channel irons extending lengthwise of the sec¬ 
tions provides ready means of joining additional sections. 

This frame is suitable for any size exchange, and is the standard 
type for 100 or more lines up to any capacity. Protectors can be added 
in banks of 20 pairs at any time. 

A good ground connection must be provided for the frame. Use a 
No. 6 copper wire. 

Cook’s Intermediate Distributing Frame should be used in multiple- 
system exchanges having a few hundred lines or more, as it is very ad¬ 
vantageous in distributing the amount of work equally between the var¬ 
ious operators on the board. In appearance this is the same as the main 



























































LINE AND CABLE CONSTRUCTION 


489 


frame, except in place of protectors are mounted groups of terminals. By 
the aid of an Intermediate Distributing Frame, certain operators will not 
be overworked while others have a lack of work, as is usually the case in 
exchanges of any size where an Intermediate Distributing Frame is not 
used. 

In a Multiple Switchboard the answering jacks and line signals gen¬ 
erally branch off from the main line circuits which include the multiple 
jacks. By using an Intermediate Distributing Frame these branches to 
the answering jacks and line signals, may be interchanged between the 
lines, so that any line may be answered at any position on the switch¬ 
board. In this manner the total number of very busy lines may be dis¬ 
tributed between the various operators so as to divide the work equally 
between them. 

Cook’s Intermediate Distributing Frame having distributing blocks 
on one side, preferably on the answering jack side, is very advantageous 
in making the cross connections from one side of the frame to the other. 
There is a considerable space between the distributing blocks so that a 
person’s arm may be inserted into the frame and then moved either ver¬ 
tically or horizonally throughout the entire extent of the frame. 

The uprights of the frames are of angle iron and are securely bolted 
to an angle iron bafee, making a rigid and substantial frame work. To 
the uprights are secured horizontal strips of channel iron extending from 
front to back. These horizontal channel irons support the distributing 
blocks and strips. 

The vertical distributing strips on the multiple jack side of the frame 
hold the parts of the frame together rigidly and provide a very substan¬ 
tial construction. 

The main vertical angle irons of the frame are provided with insulat¬ 
ed distributing rings, which, in connection with the rings directly back of 
the distributing blocks, keep the jumper wires in the frame away from 
any of the iron portions. 

Iron racks or runways are provided to carry the cables f rom the 
board to the frames. A 100-line outfit is shown in Fig. 599. The usual 
method of connecting the equipment, is such that the incoming line wires 
connect directly to the protector terminals, and then connect by means of 
jumper wires with the terminals of the switchboard cable. 

In some systems the protectors are located on the switchboard side 
of the frame, the line side being equipped with plain terminals. This 
method affords the same protection to the switchboard and apparatus, 
except that the jumpers are not protected except by such fuses as may be 
placed in the boxes outside. 

One of the largest manufacturers furnishes the following informa¬ 
tion regarding forming up the switchboard cables, as it is sometime^ 
necessary to form these to connect to the arrester or intermediate frames. 

Switchboard Cabling .—A ter the cables from the switchboard are 
laid in their permanent positions the free ends should be lined up parallel 
to the arrester strips to which they are to be attached. Each pair of 
conductors in these cables are provided with distinguishing colors arrang¬ 
ed in a definite code so that the switchboard drops and arrester terminals 
can be readily wired together and the same uniformity kept throughout. 


490 


TELEPHONOLOGY 



Fig. 599. 


A color code used by The Dean Electric Co., is as follows: each wire 
from 1 to 20 inclusive, being twisted with a white mate, 21 to 40 a red 
mate, and 41 to 50 a black mate. 


1— Blue 

2— Orange 

3— Green 

4— Brown 

5— Slate 

6— Blue-white 

7— Blue-orange 

8— Blue-green 


18— Brown-white 

19— Brown-slate 

20— Slate-white 

21— Blue 

22— Orange 

23— Green 

24— Brown 

25— Slate 


35— Green-white 

36— Green-brown 

37— Green-slate 

38— Brown-white 

39— Brown-slate 

40— Slate-white 

41— Blue 

42— Orange 


















































LINE AND CABLE CONSTRUCTION 


491 


9—Blue-brown 

10— Blue-slate 

11— Orange-white 

12— Orange-green 

13— Orange-brown 

14— Orange-slate 

15— Green-white 

16— Green-brown 

17— Green-slate 


26— Blue-white 

27— Blue-orange 

28— Blue-green 

29— Blue-brown 

30— Blue-slate 

31— Orange-white 

32— Orange-green 

33— Orange-brown 

34— Orange-slate 


43— Green 

44— Brown 

45— Slate 

46— Blue-white 

47— Blue-orange 

48— Blue-green 

49— Blue-brown 

50— Blue-slate 

51— Blue-orange-white 

52— Blue-orange-white 


(The last two pairs are spares with a white and red mate respectively 
which can be used in case any of the regular pairs should become defec¬ 
tive.) 

We wire pair No. 1 of a cable to the terminals of Drop No. 1 of the 
switchboard, the plain colored conductor (white in this case) going to the 
tip spring of the jack, while the wire having the distinguishing color is 
connected to the sleeve of the jack. The wiring remains uniform in our 
switchboard regardless of any special numbering of the drops and jacks. 
In this way, one cable will include the drops No. 1 to No. 50 inclusive, 
while No. 51 to No. 100 inclusive will be wired with the second cable, 
drops No. 101 to No. 150 inclusive will be wired to a third cable, etc. The 
color code for distinguishing the pairs is the same in each cable, and it is 
an easy matter when installing to determine the group of drops included 
by a particular cable by tracing the run to the switchboard. 

As soon as the cables are properly arranged along side the arrester 
terminals and each marked at the point where the first pair of wires is to 
leave for its corresponding terminal clips, the outer braidings and paper 
coverings can be removed so as to expose the twisted pairs of wires. In 
marking these points it is best to arrange to remove about one inch more 
of the covering than is actually necessary to allow the first wire to clear, 
thus giving room for a binding called a “butt.” The latter is made as 
illustrated in Fig. 587 by binding a stout linen tape, one quarter of an 
inch in width, tightly around the exposed edge of the braiding. The free 
end “b” of this tape should be inserted in the loop first formed and pulled 
under the binding by drawing on the end “a”, after which both ends are 
cut away so as to produce a finished job. 

The exposed wires of the cables should now be boiled in beeswax or 
a combination of beeswax and paraffine, up to the butt and including it, 
until all bubbles in the liquid disappear. The wax serves a double pur¬ 
pose, as a moisture repellant and a means of preventing the insulations of 
the wires from loosening up while per orming the succeeding operations. 
All surplus wax should be removed from the wires by lightly whipping 
the cable end against a board immediately upon taking the latter from the 
boiling liquid. A temporary forming board, made from a wide piece of 
soft wood, should now be provided and marked off with the distance 
between the clips on the arrester or terminal frame to which the cable is 
to be fastened. A distance equal to the space which the cable is to set 
back from these clips should also be marked on this forming board. The 
former distances are shown as “CC” in Fig. 587 and should be laid^ off 
uniformly, while the latter distance is shown at A . Drive nails d , 
“d”, “d”, etc., into the board at the points just marked so that the cable 
wires can be bent around the same in making the form. The cables 


492 


TELEPHONOLOGY 


should now be clamped as shown in the illustration and the wires brought 
around the nails following the color code, and bringing the No. 1 pair 
around the nail “d” nearest the butt of the cale and anchoring it to the 
nail by making one complete turn around the latter, etc. 

The loose wires are bound together with a single length of bees-wax- 
ed linen twine by what is called a lock stitch lacing formed as shown in 
Fig. 589. This lacing, when properly made, requires that the free end of 
the twine be drawn under the loop thereby locking each lace and prevent¬ 
ing it from loosening. In starting the stitch a knot is first taken next to 
the butt of the cable as shown in Fig. 589 and after the last stitch is 
taken the lacing should be securely fastened at the end of the form. 
After lacing up the form, the projecting pairs of wires should be cut off 
even, leaving a sufficient length “a” to properly fasten to the terminals, 
allowing an inch for skinning. 

Care should be exercised in doing this skinning operation as a small 
nick in a wire is sufficient to cause a break as soon as the wires are 
handled or subjected to vibration. 

The wires and cables should now be permanently fastened in place 
on the frame, either by small leather straps bound around the cable and 
secured by screws or by binding with waxed lined twine. 

In making the subsequent connections to the arrester strips, the 
wires with the colored insulation should always be connected to the upper¬ 
most clip of a pair of terminals as it comes from the tip spring of the line 
jack and goes to the tip side of the line circuit. The mate should go to 
the next clip, etc. 

The bare ends of the wires are threaded through the holes in the 
clips up to their insulated covering and bent back, or, if notched clips are 
used, the wire should be wrapped once around the notched portion of the 
clip. Be sure to have the hole or notch free of the insulation of the wire, 
also that the wire be bright and a good connection made. 

Acid must not be used under any consideration in soldering as it 
forms a good conductor for the voice and generator currents and will 
result in cross talk and generator noise by leaking from one line to an¬ 
other. Resin core solder is the safest material for soldering as the resin 
flux is fed in the right quantity for good work and the latter is non-corro¬ 
sive and an insulator. After soldering, the free ends of the wires should 
be cut off close to the clips and each joint inspected to discover any imper¬ 
fect Work. 

If cross connecting strips are provided on the arrester frame, they 
will be a great convenience in connecting any switchboard drop to the 
line without;disarranging the cables or terminal wiring of the exchange. 
The connecting wires between the terminals are called jumper wires and 
can be changed from time to time as different lines are terminated on 
different drops or subscribers’ telephones are moved to different locations. 

These jumper wires come in twisted pairs, one of the conductors of 
a pair having a white insulation, and the other a red insulation, the form¬ 
er always being used for connecting together the tips of the circuits and 
the latter the sleeves. 

Extreme care should be used in running these jumper wires that the 
colors be connected straight through, never connecting a red wire of a 
jumper pair to a tip wire on the cross connecting strip as this would 
reverse the tip and sleeve line conductors with respect to the switchboard. 


LINE AND CABLE CONSTRUCTION 


493 


vinn-Jtu a , rr ,f te 5 fr 1 ai ?f. s ar f provided with jumper strips and jumper 
rings, the latter for holding the jumper wire when making a cross connec- 


In common battery systems a relay rack is nearly always used, and 
is requires an additional set ot cables. The wiring varies with each 
s> stem but m general conforms to the examples previously given. A 
view of a terminal room equipped with Western Electric Co.’s apparatus 
I s shown in Fig. 600 which shows the relay rack, intermediate and main 

irames and cabling. The actual arrangement varies with each installa¬ 
tion. 



Li 






1 

- 






— 

3H 




Fig. 600. 

The growing tendency is to use as much cable as possible in outside 
construction. Although the first cost is greater than that of the open wire 
plant, still the decrease in cost of maintenance will in a few years more 
than counter-balance the first outlay. 

*“The arguments in favor of cable conductors are too well known to 
require more than the briefest mention: perhaps the strongest, from the 
point of view of the electrical companies is the great unreliability of the 
overhead conductors, subject, as they are to all changes of the weathe r, 

“Data and cuts from XVII Handbook. Copyright 1906, by Standard Underground 
Cable Company.” 
















































































494 


TELEPHONOLOGY 


and at times entirely disabled by wind, snow or sleet, causing the entire 
suspension of business for hours at a time, and costing hundreds of thou¬ 
sands of dollars annually for repairs. Considered from the point of view 
of the public, overhead wires are also objectionable, disfiguring the 
streets, obstructing firemen in their duties, and constantly menacing life 
and limb. The contrast in the appearance of the same street with over¬ 
head wires and with under-ground cables is graphically shown in the 
illustration in Fig. 601 which represents Broadway, N. Y., as it appeared 
in 1887, while an illustration of Broadway as it is today is shown in Fig. 
602.” 



Fig. 601. 

While a complete system of underground cable is the best guarantee of 
the practical control of the telephone business, the use of aerial cable also 
affords immunity from wind, snow and sleet, and it may be safely assert¬ 
ed that in any case where the extent of the line exceeds six ten pin cross- 
arms it is much better and cheaper to use cable. 

By improved methods the cost of cable has been gradually decreased, 
with the result that today it is cheaper to lay underground or use aerial 
cable than to use open wire circuits, when the cost of maintaining the 
aerial circuits for three or four years is considered. 

Where the number of conductors is great, as is the case in exchanges 
of considerable size the relative saving between cable and open wire con¬ 
struction is enormous. 

“Data and cuts from XVII Handhook, Copyright 1906, by Standard Underground 
Cable Company.” 









LINE AND CABLE CONSTRUCTION 495 

There are several large companies today making cable suitable for 
telephone work. The information, method of construction and data 
given in this chapter, illustrates the product of The Standard Under¬ 
ground Cable Co., which is one of the oldest and most reliable of these 
concerns. Their product has been developed over a period of more than 

.f, > years, and some of the largest systems in operation are furnished 
with their equipment. 



Fig. 602. 

“Aerial telephone cable is usually furnished in No. 19, No. 20 or No. 
22 B. & S., guage. No. 19 is commonly used for undergound work, while 
No. 20 and No. 22 is used for aerial. In cables of this description each 
conductor is insulated with one or two wraps of paper. Paper is used as 
the insulating covering because it lowers the capacity of the cable, which 
is highly desirable in telephone work. For this reason it is desirable to 
apply the paper so as to include as much air as possible, consistent with 
the prescribed size of the cable. Therefore the bunch or core of wires is 
preferably left “dry core,” i. e. not saturated or filled with insulating 
compound.” 

“In some cases the cables which branch or distribute from “dry core” 
cables are made with saturated core so that there may be no danger of 
moisture gaining access to and destroying the insulation of the dry core 
mains. It is apparent that injury to the sheath of the saturated core 
cable will destroy but a small portion of it, whereas a dry core cable 
under the same conditions would in the majority of cases become a total 

‘‘Data and cuts from XVII Handbook, Copyright 1906, by Standard Underground 
Cable Company.” 











496 


TELEPHONOLOGY 


loss, for the substance entering the sheath would quickly spread through 
the cable, and it would be necessary to cut out or replace a great many 
feet each side of the break.” 

“The form of construction now universally used in telephone cable is 
that known as “Twisted Pairs,” the individual conductors, after receiving 
their proper covering of paper, being twisted together in twos. 
After the wires are so paired, they are assembled into a bunch or core: 
the core is wound with paper tape and then thoroughly baked in specially 
designed apparatus, and finally it is provided with a lead cover.” 

“Each twisted pair constitutes a “metallic circuit” from the exchange 
switchboard to the subscriber’s telephone, and as each leg of the circuit 
is subjected to the same influences from the adjacent conductors, occupy¬ 
ing the same position relative thereto, a complete neutralization or bal¬ 
ance of inductive interference is secured. If the twist is short, say one in 
three or four inches, there is no cross talk whatever. In order to facili¬ 
tate identification of the individual wires of a pair, and to avoid crossing 
the pairs in splicing, they are covered with paper of different colors: for 
example, one wire may be covered with red paper, and another with blue 
paper.” 

“Dry core cables are especially susceptible to moisture, and the ends 
must always be sealed with solder. Where they terminate in actual ser¬ 
vice the ends must be protected by pot heads, or other suitable terminals, 
as described later.” 

“The highest class of telephone cable, and that generally used for 
telephone work by the large Bell and Independent telephone companies, is 
represented by the following condensed specifications: 

“Copper conductors No. B. & S. G., 98 per cent conductivity: insula¬ 
tion to consist of one or two paper tapes: conductors to be twisted in pairs 
(one or two pairs to have colored paper) the length of the twist not to 
exceed 3": pairs to be formed into a core arranged in reversed layers: the 
core to be dry (unsaturated) except for two feet at each end: the sheath 
to be free from defects, to be of lead alloyed with 21/2 to 31/2 per cent tin, 
and a uniform radial thickness of 1-12" for 1 to 49 pair, 3-32" for 50 to 
99 pairs, and 1-8" for 100 to 150 pairs: insulation resistance at least 100 
megohms per mile when laid, spliced, connected to terminals, ready for 
use; mutual electrostatic capacity (any conductor measured against its 
mate with the remaining wires grounded to the sheath) .054 average and 
.060 maximum. The mutual capacities stated are equal respectively to 
.08 and .085 mfs. per mile regular capacity (each conductor against all 
others grounded to the sheath.)” 

“Specifications for aerial cable may be so modified as to permit of the 
use of No. 22 B. & S. G. conductors with an electrostatic capacity of .069 
average and .078 maximum mutual, the thickness of lead being slightly 
reduced throughout. The decreased efficiency of the talking qualities is 
comparatively immaterial, where short lengths of cable are used.” 

“The following will be of interest to telephone cable users in compar¬ 
ing the relative values of telephone cable in terms of cost and terms of 
relative “talking value,” and may give them a better appreciation of the 
factors to be considered and the care to be observed in order to insure a 


“Data and cuts from XVII Handbook. Copyright 1906. by Standard Underground 
Cable Company.” 






LINE AND CABLE CONSTRUCTION 4 97 

correct decision as to such relative values. The specifications should be 

exact and definite on all points, and particularly as to electrostatic 
capacity.” 

A. given standard of efficiency in transmission of sound is more 
economically obtained by the use of No. 19 B. & S. G. conductor than with 
any smaller size. As between No. 20 and No. 22 whether for overhead 
or underground use, it should be remembered that No. 20 insures a great¬ 
er immunity from service interruptions resulting from mechanical injury 
to the conductors.” 

‘‘The following figures from the American Telepone & Telegraph 
Co.’s (Bell Long Distance) specifications show conductor resistance allow¬ 
ed per mile for conductors of various sizes, and the figures take into 
consideration and make proper allowance for the increased length of the 
conductors due to twisting in pairs and laying up into cable form: 

22 B. & S. G., 95 Ohms; 20 B. & S. G., 60 Ohms; 19 B. & S. G., 47 
Ohms. 

Two wrappings of paper applied spirally in opposite directions add 
somewhat to the cost of the cable, but are mechanically superior to one 
wrapping. Costly experience has demonstrated this many times.” 

‘‘There are two methods for testing for electrostatic capacity. First, 
the regular or old trade standard method of testing to ground with the 
connections made in the same manner as in a test for insulation resist¬ 
ance, namely, One wire measured against the remaining wires grounded 
to th* 1 sheath.” 



Fig. 603. 


“Second: an entirely different test, for mutual electrostatic capacity, 
in which one wire is measured against its mate, the remaining wires 
being grounded to the sheath. Fig. 603 shows graphically the relative 

“Data and cuts from XVII Handbook. Copyright 1906, by Standard Underground 
Cable Company.” 

32 
















498 


TELEPHONOLOGY 


sizes of two cables alike in other respects, and which tested by the differ¬ 
ent methods (as also graphically illustrated) show ‘.08 capacity’: but 
which when both are tested by the regular method with one conductor 
against the remaining wires grounded to the sheath, show .08 microfarad 
per mile for the larger cable and .12 microfarad per mile for the smaller.” 

“If these two methods of testing were applied to identical cables, the 
average relation between the two methods would be shown as follows: 


Average 

Regular Capacity 
(to ground). 


Average 

Mutual Capacity 
(to mate). 


.08 

.10 

.12 

.14 

.16 

.18 


equals 


.054 

.066 

.08 

.093 

.107 

.12 


“This is a feature of telephone cable specifications which is of im¬ 
mense importance to all buyers and users of telephone cable, especially 
those who operate moderate or long lengths of cable, yet its full signifi¬ 
cance is seldom grasped by cable purchasers.” 

“For the purpose of obtaining relative efficiencies of telephonic 
transmission through cables of different conductor resistances and elec¬ 
trostatic capacities, Sir Wm. Preece’s “KR” law stands today re-affirmed 
and may be expressed thus: 


Capacity X Resistance = C. 

“In which the various values obtained for C (from cables of like 
length but different electrostatic capacities and conductor resistances) 
may be used to compare the relative talking values of such cables.” 

“This law is based upon the fact that as the resistance of the conduc¬ 
tor increases, it becomes a poorer talking circuit. Similarly when the 
electrostatic capacity increases, the talking circuit is poorer and speech is 
transmitted less perfectly, and when it decreases, the reverse is true. 
Now since the value of a talking circuit in a cable (for speech transmis¬ 
sion) depends upon both electrostatic capacity and conductor resistance, 
the relative values of talking circuits in different cables may be observed 
by comparing the product of electrostatic capacity and resistance in the 
one cable, with the product of electrostatic capacity and resistance in the 
other. All combinations—of electrostatic capacity multiplied by resist¬ 
ance—which give the same product (or value for C) would have the same 
telephonic transmitting value. Any combination which has a smaller 
product will have a better transmitting value, and any combination which 
has a greater product will have a poorer transmitting value.” 

“Thus, if we take a specific case of ten miles of cable No. 19 B. & S. 
G. conductor having conductor resistance of 47 ohms per mile, and an 
electrostatic capacity of .08 microfarads per mile, the application of the 
formula would show the following results.” 

“Data and cuts from XVII Handbook, Copyright 1906, by Standard Underground 
Cable Company.’* 

















LINE AND CABLE CONSTRUCTION 


499 


“The total electrostatic capacity of the circuit would be .08 X 10 
equals .8 microfarads: and the total resistance, 47 X 10 equals 470 ohms, 
and when these are substituted in the formula we have .8 x 470 equals 
376.” 

“As any other cable whose electrostatic capacity multiplied by its 
conductor resistance equals 376, has the same value for telephonic trans¬ 
mission, it will be observed that not more than 5% miles of No. 22 B. & 
S. G. cable, .12 microfarads per mile, could be used if the service is to be 
of the standard given by 10 miles No. 19 B. & S. G., .08 cable: and this is 
shown by the following application of the formula.” 

“The total electrostatic capacity of the circuit would be .12 X 5.75 
equals .69 microfarads: and the total conductor resistance, 95 X 5.75 
equals 545 ohms, and when these are substituted in the formula, we have 
.69 X 545 equals 376. It should be remembered that doubling the length 
of the cables in the above example, would change the relation in “talking 
values” since the length enters into the calculation as squares and not as 
simple fractions.” 

“The following table shows in convenient form the relative values of 
electrostatic capacity multiplied by the resistance, for 10 miles of cable 
with various conductors and electrostatic capacities in general use: 


VALUES OF C FOR TEN MILES OF CABLE. 


& S. G. 

Ohms per Mile. 

Electrostatic 

Capacity 

per Mile. 



.08 

.10 

.12 

19 

47 

376 

470 

564 

20 

60 

480 

600 

720 

22 

95 

760 

950 

1140 


“The following table shows the various combinations of length, ca¬ 
pacity and resistance of telephone cables required to produce the same 
arbitrary talking value. In other words, it will be observed from this 
table that a telephone cable 2,656 feet long, made up of No. 19 B. & S. G. 
wires having a capacity of .08 mfs. per mile, will have the same talking 
value as 877 feet of telephone cable made up of No. 22 B. & S. G. wires 
having a capacity of .12 mfs. per mile.” 

LENGTHS OF VARIOUS CABLES FOR SAME TALKING VALUE. 

Electrostatic Capacity per Mile. 
.08 .10 .12 

2656 ft. 2128 ft. 1773 ft. 

2083 ft. 1667 ft. 1389 ft. 

1310 ft. 1053 ft. 877 ft. 

“Lead covered aerial cables used generally for telephone distribution, 
require some supporting medium between the poles, as the cables them¬ 
selves do not possess sufficient mechanical strength to stand the strain. 
The necessary support is provided by galvanized steel wire,, from 
quarter inch in size up to one half inch, depending on the weight of le 
cable, length of span, etc.” _ 

“Data and cuts from XVII Handbook. Copyright 1906, by Standard Underground 
Cable Company.” 


B. & S. G. Ohms per Mile. 


19 

20 
22 


47 

60 

95 






500 


TELEPHONOLOGY 


“A fairly good factor of safety should be used in the suspension of 
aerial cables, especially in long span work in cities or towns where loss 
of life or injury to passers-by may be occasioned by the failure of the sus¬ 
pension strand.” 

‘‘The following sizes of strand are recommended for suspending 
cable, when it is desired to have 2 as the factor of safety. 

RECOMMENDED SIZES OF STRAND. 



100 foot 

120 foot 

140 foot 

160 foot 

180 foot 

200 foot 

Weight of 

Span. 

Span. 

Span. 

Span. 

Span. 

Span. 

Cable 

1% 

1.2% 

1.4% 

1.6% 

L8% 

2% 

Lbs. per foot. 

Sag. 

Sag. 

Sag. 

Sag. 

Sag. 

Sag. 

.75 

9-32 

9-32 

9-32 

9-32 

9-32 

9-32 

1.00 

5-16 

5-16 

5-16 

5-16 

5-16 

5-16 

1.25 

11-32 

11-32 

11-32 

11-32 

11-32 

11-32 

1.50 

3-8 

3-8 

3-8 

3-8 

3-8 

3-8 

1.75 

13-32 

13-32 

13-32 

13-32 

13-32 

13-32 

2.00 

7-16 

7-16 

7-16 

7-16 

7-16 

7-16 

2.25 

15-32 

15-32 

15-32 

15-32 

15-32 

15-32 

2.50 

1-2 

1-2 

1-2 

1-2 

1-2 

1-2 


‘‘The suspension wire is fastened to the sides of the poles or to the 
bottoms of the cross-arm« by suitable clips and pulled taut in place. 
There should be no splices between poles, and the ends should be securely 
fastened to prevent the possibility of slipping when the weight of the 
cable is added.” 

“The cable itself is suspended from the supporting wire, called a 
“Messenger” by means of hangers of various forms which clasp the cable 
firmly, and are provided with a hook which rests upon the messenger 
wire, the hangers being placed from two to three feet apart. When 
installing aerial cables, a Leading up” wire is stretched from the bottom 
of one pole to the messenger wire on the starting pole. A rope is fasten¬ 
ed to the end of the cable and carried along the messenger to the point 
where the cable is to reach, and is run through a snatch hook down the 
terminal pole to a second block at the bottom and thence to a capstan 
or winch. Temporary rollers are provided on the poles over which the 
rope runs or it may be held in place by wire hooks on the poles, or by wire 
hooks or loops on the messenger.” 

“Draw the cable slowly up the inclined wire and along the messeng¬ 
er, attaching hangers to the cable as it pays out, and hooking every third 
or fourth hanger onto the weight of the messenger to carry the weight of 
the cable.” 

“Linemen must be stationed at each pole to remove the hangers from 
the messenger, pass them by the messenger clamp, and replace them on the 
messenger. When the end of the cable arrives at the last span, the line¬ 
men put every hanger, as it passes the clamp at their respective poles, on 
the messenger so that when the cable is drawn over the last span all the 
hangers will be in place. The strain on the hangers which carry the 
weight of the cable while it is being drawn along, is such that they may 
loosen and tend to slip along the cable: it is therefore better to pull the 

“Data and cuts from XVII Handbook. Copyright 1906, by Standard Underground 
Cable Company.” 






LINE AND CABLE CONSTRUCTION 501 

cable in place while supporting it by “Carriers”, the wheel of the carrier 
running on the messenger, and the cable hanging in the stirrup. If car¬ 
riers are not available, wire hooks may be used. The permanent hangers 
are hooked on to the messenger, as already described, but not before the 
last span is reached: if they are put in place by linemen riding along the 
messenger wire in a “carriage’ after the cable is drawn up. In this latter 
method the loosening and slipping of the hangers is avoided and they 
remain evenly spaced on the cable.” 

“Measurements of aerial cable should always be so made that the 
joints will be at poles and not in the middle of sections between poles.” 

Platforms or steps should be provided on all poles where terminals 
are located, so as to facilitate the work and the regular inspection of the 
apparatus.” 



B Erecting Aerial Cable. 

Making Joints, Loops , Etc. —Caution. Lead covered cables are only 
as strong as the weakest spot in their entire length, and the weak spot 
often is in the joints. This is not necessarily the case, for joints properly 
made are 'ully as reliable as the cable itself, but the greatest care must be 
exercised to secure perfect results. 

In view of the importance of the joints—the most important part of 
the cable installation—employ only experienced and careful workmen. 
Have every splice inspected by the foreman, (who should be thoroughly 
competent to detect defective workmanship) and consider no joint com¬ 
plete which has not received his approval. 

“An expert lineman may sometimes be used to make and insulate the 
wire joints but never allow the solder wipe-joint to be made by any one 
who is not thoroughly experienced in such work. If a cable splicer is not 
available, a first class plumber will answer, provided extra careful inspec¬ 
tion is given to his work. Scrupulous cleanliness is an essential to good 
results, and the workman’s hands should be as free from perspiration as 
possible. A little moisture from the hands may result in poor insulation 
resistance, especially in the case of dry core telephone cables. 

“Data and cuts from XVII Handbook. Copyright 1906, by Standard Underground 
Cable Company." 








502 


TELEPHONOLOGY 


“Wherever possible, each section of multiple conductor cable should 
be tested for continuity and grounds before making the joint, and again 
after the joint is finished. 

“General Directions for Making Joints on Lead Covered Cables .— 
The directions here given apply to any cable locations but more particu¬ 
larly to cables in underground conduits and manholes. 

“The cables are usually left by the pulling-in gang without ^ very 
much reference to final arrangement, and it should be the jointers’ first 
duty to inspect the cable thoroughly, from the edge of the duct to the 
sealed end, in order to discover any mechanical injury or intrusion of 
moisture. Where there are several cables to be jointed in one hole, care 
must be exercised that the corresponding incoming and outgoing sections 
are spliced together. Absurd as it may seem, mistakes are sometimes 
made on this point. After placing protectors in the mouth of the ducts, 



A Drawing in Underground Cables. 


the cables should be neatly bent and stored around the sides of the man¬ 
hole, and the ends brought into position for jointing at the designated 
point, which should always be such that the joint, when finished, will lie 
between two supports or hangers so that there will be no strain on the 
joint itself when completed and stowed away. In single conductor cables 
where a “butt” joint is used, the cables should overlap very slightly if 
any; but in multiple conductor cables where the wire joints must be 
“staggered” (i. e. not all opposite each other) the cables should overlap 
sufficiently to allow for the proper distribution of the wire splices. 

Removing Moisture. —When the ends of cables have been allowed to 
lie for any length of time in manholes where there is water, a very slight 
imperfection in the soldered end will admit more or less moisture to the 


“Data and cuts from XVII Handbook, Copyright 1906, by Standard Underground 


Cable Company.” 


















LINE AND CABLE CONSTRUCTION 


503 


insulation. A careful examination should always be made, and, if any 
moisture is evident, the cable should be cut back a little at a time until all 
evidence of moisture disappears, care being taken not to cut back so far 
as to render it too short to make the joint. When no more cable can be 
cut off, and moisture is still present, as shown by bubbles when the cable 
is dipped into hot insulating compound, apply heat to the lead cover of the 
cable, beginning at the point nearest the duct and very slowly approach¬ 
ing the end of the cable, the object being to drive all moisture to the open 
end. Wherever it is allowable, a furnace or gasoline torch may be used 
for this purpose, and if the cable is covered with saturated fibre, a metal 
screen should be interposed between the flame and the cable to prevent 
ignition of the fibre. If the use of a furnace or torch is forbidden, or is 
unsafe on account of the presence of gas, the heating should be effected 
by pouring very hot insulating compound over the cable, catching it in a 
vessel held underneath. Where there is still any doubt as to freedom 
from moisture, it is best to make a careful insulation test before the joint 
is made. This test may indicate the necessity of replacing the cable sec¬ 
tion. 

“Never cut off the end of one section until sure that there is no mois¬ 
ture in the other section. —You will thus have an opportunity to change 
the location of the splice in case the other end must be cut back for mois¬ 
ture. 




C Feeding Cable through Manhole. D Underground ducts in trench. 


“Scoring the Lead.— When the cables are placed in position and 
ready for the jointing, the ends should be marked at the point to which 
the lead is to be removed, and scored or cut entirely around.. This cutting 
is easily and accurately accomplished by means of a special tool which 
works on the principle o~ an ordinary pipe cutter. 


“Most jointers accomplish the same result by means of a plumber’s 
chipping knife and hammer, marking the lead but. being careful not to 
cut entirely through to the insulation which might thereby be damaged. 

"Removing the Lead.— The lead sheath is then cut length wise of the 

“Data and cuts from XVII Handbook, Copyright 1906, by Standard Underground 


Cable Company.” 










504 


TELEPHONOLOGY 


cable from the circular score to the end, by the chipping knife, and the 
piece of lead is removed with a pair of pliers. In making the longitudinal 
cut which goes entirely through the lead, great care must be exercised not 
to injure the insulation. The knife should be held at such an angle that 
it will go through the lead, tangent to the insulation, (i. e., so that the 
knife will pass between the insulation and the lead and not cut the insula¬ 
tion), or a special tool furnished by the manufacturer may be used. 

“After the lead has been removed, the parts where the lead was 
scored should be carefully examined and all sharp edges or projections, 
which might tend to penetrate the insulation of the cable, should be 
removed by a knife, or the lead should be slightly bellied out by some blunt 
instrument such as the end of the pliers. 

“The Lead Sleeve .—When the lead covers of the two cable sections 
have been thus treated a lead sleeve, which will later be used in jointing, 
is slipped over the more convenient end and pushed back out of the way. 
The lead of this sleeve should be at least as thick as the lead of the cable 
itself, and, in view of its exposed position, may (in the case of thin lead 
on the cable) be made somewhat heavier to give greater mechanical 
strength. 



Fig. 604. 

11 v *. 

“Before slipping it on the cable, each end of the sleeve is thoroughly 
scraped with a shave-hook or knife, for a length of about two inches, and 
the cleaned portion thoroughly smeared with some convenient flux, 
(usually a tallow candle,) which, by preventing the formation of the 
usual film of lead salts, insures a close union of the lead and the wiping 
metal which is used to make the joint between sleeve and cable sheath. 
The internal diameter of the sleeve should exceed the diameter over the 
lead of the cable by 1" to 114". The operation of wiping the joint is shown 
in Fig. 604. 

“The following table is somewhat more liberal in allowances for 
clearance between inside of sleeve and outside of cable, but it is fairly 
representative of average practice in this respect as well as in the sleeve 
lengths. 

“Data and cuts from XVII Handbook, Copyright 1906, by Standard Underground 
Cable Company.” 







LINE AND CABLE CONSTRUCTION 


505 


Approximate data as to lead sleeves, weights of solder and 
lpound for straight joints (two-way.) 

splicing 


Outside 

Inside 

Length 

Gals. 

Wiping 


Diam. 

Diam. 

of 

Ozite 

Solder 

• 

of cable 
in Mile. 

Sleeve 

Sleeve 

per 

Joint. 

per 

Joint. 


Up to 800 

U/2" 

14” 

.15 

1.5 lbs. 

Telephone 

801 — 1200 

2 

16” 

.25 

2.5 lbs. 

1201 — 1600 

2l/ 2 ” 

18” 

.40 

3.7 lbs. 

and 

1601 — 2000 

3” 

20” 

.7 

5.0 lbs. 

Telegraph 

2001 — 2400 

3V 2 " 

22” 

.9 

6.3 lbs. 

Cable. 

2401 — 2800 

4” 

24” 

1.3 

7.6 lbs. 


2801 — 3200 

4i/ 2 ” 

26” 

1.8 

8.3 lbs. 


Note: Ozite is not used in paper insulated telephone cable splices. 



Sleeve before wiping. 


“Joints on Bunched Cables. —“Bunched Cables” so called, are used 
for telegraph, telephone and signal circuits, and contain, in the case of 
telegraph cables, any desired number of conductors up to two hundred, 
usually of No. 14 B. & S. G. copper, each wire insulated to a diameter 
(over the insulation) of 5-32” or 6-32”; the insulated wires are arranged 
in layers with a spiral twist, each layer being twisted in a direction oppo¬ 
site to the next adjoining. In telephone and signal cables the wires are 



Fig. 605. 


smaller, No. 22, No. 20, No. 19 or No. 18 B. & S. G., each wire being insu¬ 
lated (but with different colored paper) are twisted upon each other once 
in every 21/2 to 3” so as to form a “Pair”. The twisted pairs are then 
formed into a “Core” containing any desired number of pairs, usually in 
multiples of five, up to a miximum of six hundred._ 

“Data and cuts from XVII Handbook, Copyright 1906, by Standard Underground 
Cable Company.” 








506 


TELEPHONOLOGY 


“Arrange the cables in position for jointing, allowing the ends to 
overlap from twelve to twenty-four inches, according to the number of 
wires or pairs in the cable. In case the insulation is dry paper, the mass 
of wires must be thoroughly saturated with hot paraffine, before separa¬ 
tion, to prevent the paper from untwisting, but more particularly to pre¬ 
vent the absorption of moisture by the paper. Slip the lead sleeve over 
one end of the cable, strip off the lead and bend the wires back, layer by 
layer, until the innermost wire or layer is reached. Choose a wire or pair 
from one of the ends, and its mate from the other, and slip a small paper 
sleeve, three inches long, (See upper part Fig. 605), on the more con¬ 
venient end. Having determined the location of the wire splice, cut off 
the surplus after allowing an overlap of 3" for twisting the wires to¬ 
gether; draw the two ends sung, (not too tight), strip off the surplus 
insulation, twist the bare wires together and tighten with a pair of pliers; 
cut off the surplus wire, bend the ends down on the main wire and slip 
the insulating sleeve over the splice, all as shown in lower part Fig. 605. 



Fig. 606. 

“The term “mate” as above used, needs further explanation: In 
twisted pair telephone cable, it may be any pair in a corresponding layer, 
care being taken to splice red to red, and blue to blue, so as not to cross 
the colors, for such crossing may lead to confusion when testing out; 
equal care must be used not to split the pairs, i. e., not to connect the wires 
of one pair with the wires of several pairs in the opposite section, for that 
too will cause trouble in testing out and destroys the anti-induction quali¬ 
ties of both circuits. In a telegraph cable, “mate” means any wire in a 
corresponding layer, unless each layer has an identifying wire or marker, 
in which case the identifying wire must be first connected and the first 
adjoining wire on one side with the corresponding wire on the other side, 
(passing around to right or left) in each layer, so as to preserve the con¬ 
tinuity of identification and the same relative position of all other wires 
in each layer, throughout the whole length of the cable. 

“While paper sleeves are used in joints of telephone cables, cotton 
tubing is often used in the case of telegraph cables. 

“In order to make the finished joint as small as possible, it is neces¬ 
sary to distribute the wire splices evenly along the entire length of the 
cable joint, no two adjacent wires having joints opposite one another. 
(See Fig. 606.) 

“When all the wires are joined and insulated, the entire splice should 
be thoroughly boiled out with paraffine, and wrapped with muslin cut in 
strips about 3" wide. This serving enables the workman to draw the 
joint down to the smallest practicable size consistent with the size of the 

“Data and cuts from XVII Handbook, Copyright 1906, by Standard Underground 
Cable Company.” 











LINE AND CABLE CONSTRUCTION 


507 


lead sleeve. The cotton serving should be thoroughly boiled out, and the 
lead sleeve wiped to the cable sheath, in a manner already described. 

“We do not recommend filling the joints on dry paper telephone 
cables. 

“The wires to be tapped or branched are picked out at the splice, 
usually by electrical tests, and the two main wires together with the 
branch wire are joined under the same insulating sleeve, the lead joint 
being made in the shape of a Y as heretofore described. 

“In working on dry paper insulated bunched cables, observe the fol¬ 
lowing precautions: 

“Never leave the ends exposed to the atmosphere, or open in man¬ 
holes, if possible to avoid it; and when this is unavoidable in the process 
of work, soak the exposed paper carefully with hot paraffine. 

“Start at one end of a cable (not at intermediate sections) and put 
on a “Test-Cap” before making any joints. A test-cap is made by strip¬ 
ping all of the insulation from the end of each wire for a distance of six 
inches, bunching all of the wires together, carefully insulating the bunch, 
and protecting it from the weather by a lead cap, soldered or taped to the 
lead sheath of the cable. 

“When starting to splice at the first break in the cable, a test with a 
telephone receiver in series with a few cells of dry battery, between any 
wire and the lead sheath of the cable, will at once show if a “ground” 
exists on any wire in the cable. 

“Connecting one side of the battery to one wire of the cable and the 
other side of the battery to one side of the receiver and touching the other 
wires, in succession, with the free wire of the receiver, a decided click is 
heard if the wire under test is continuous to the test cap. If no sound is 
heard in the receiver, or only a very faint click, it is good evidence that 
the wire is open or broken. 

“In making joints in manholes or elsewhere, these tests should al¬ 
ways be made to the test cap, and ahead through the next section, which 
has been provided, at the next joint, with a temporary test cap. Ground¬ 
ed wires, which are very rare, should be identified at the test cap and sep¬ 
arated from the bunch so that the remaining wires will show clear. 

“Defective wires or pairs in one section should be joined to defective 
wires or pairs in the next section. If this is not done and the wires aie 
connected at random, without test, the cable when entirely completed, 
may be found with many defective pairs or wires whereas proper atten¬ 
tion to this detail might in many cases save every wire or pair except one. 

“All cable manu acturers provide extra wires in bunched cables, over 
and above the number ordered by the customer, in order to provide for 
possible breaks in the wires of the cable. If care is exercised in the splic¬ 
ing and tests referred to above, the extra wires will always suffice for 
such cases of open or grounded wires as arise in ordinal y manufactuie 
and installation. 

“These simple tests do not locate crossed wires, but crosses in cables 
are very infrequent and can be readily located after the work is otherwise 
completed.” (See Chapter 9.) _ _ 

“Data and cuts from XVII Handbook, Copyright 1906, by Standard Underground 
Cable Company.” 





508 


TELEPHONOLOGY 


It is more economical to install large main leads of telephone cable, 
with branches of smaller cable extending to various points of distribu¬ 
tion, than it would be to extend separate cables from the exchange to each 
distributing point. This plan of cable distribution, however, requires 
cable splices at each junction, and many exchanges have no one at their 
command capable of forming a cable splice or wiping a joint, and to 
obtain skilled cable splicers adds materially to the cost of installing cable. 

A simplified method of forming a splice or of making a joint, which 
would not require labor particularly skilled, is not only a great conven¬ 
ience, but reduces the cost of installing cable and the time taken to do the 
work. The character of a lead sleeve splice depends almost entirely upon 
the skill of the workman, and may or may not prove to be a reliable joint. 
Defects in the cable joints are sometimes due to accident. Apparatus 
which would eliminate or even reduce the opportunity for defects in the 
cable joint should be a marked improvement. 

Description. —Fig. 607 shows a junction and splicing box manufac¬ 
tured by the Moon Manufacturing Company, which is made of one solid 
iron casting, with cast iron cover and self-soldering nozzles. The cover is 
firmly secured to the box by heavy machine screws which do not extend 
through to the inner side of the box. The joint is made by a one-piece 
rubber gasket, between two perfect, turned surfaces, in the same manner 
as the joint at the cylinder head of a steam engine. 

The Self-Soldering Nozzles are sealed to the cable sheaths by simply 
heating them with a blow torch, when the solder which they contain melts 
and runs to a lower level, uniting with the tinned surfaces of the nozzle 
and the cable sheath, casting a perfect, solid joint. No particular skill is 
required to perform this work, and the same result is obtained with each 
nozzle. The lower portion of the junction box may contain a small quan¬ 
tity of compound or paraffine which surrounds the cable wires and 
covers the ends of the cable sheaths, and prevents moisture from pene¬ 
trating into the cable when the box is opened at any time. The cable 
wires extend above the compound, where they may be inspected or tested. 

Drying out the Box. —A screw plug at the top of the box affords a 
place for ventilation, while the air in the box is being dried out, which is 
performed by warming the box, either with a blow torch or with the hot 
paraffine. When the screw plug is replaced (before the box cools) the 
junction box is sealed up like a fruit jar. 

The Cables are not Exposed. —It must be understood that to open the 
box, by removing the cover, does not mean that the cable has been opened 
or exposed, for this is distinctly not the case. The compound covers the 
cable sheaths, and the cables are thus practically pot headed. Only the 
wire splices are exposed. With ordinary sleeve splices, where the joint is 
opened for any reason, the cable ends are exposed and no protection is 
afforded. 

Providing for Extensions of Cable. —The junction box may be pro¬ 
vided with extra openings for additional cable, in contemplation of future 
extensions. These openings are sealed temporarily by a screw plug, 
which may be removed at any time and self-soldering nozzles inserted to 
receive the additional cable, and provides a simple method of making a 
splice, and a cable joint easy to form without skilled labor, practically 
eliminating the danger of forming a leaky joint, the joint being less liable 
to injury from accident and also provides means for extensions of cable 
lines or changes in cable distribution, besides establishing permanent 


LINE AND CABLE CONSTRUCTION 509 

places of opening along cable lines, where each cable may be tested and 
each wire splice inspected. 

The Combination of Terminal Head and Junction Box. (Fig. 608) 
affords means for distributing a portion of the cable conductors to the 
line wires with fuse and carbon protection. The balance of the cable con¬ 
ductors may be continued in cables of smaller size to other points of dis¬ 
tribution, making the necessary cable splices on the inside of the terminal 
head. Ample room is afforded for splicing the cable wires. By this 
means a main lead of cable may extend from the exchange, branching to 
various points of distribution. The plan of distribution may be either 
direct or in multiple, as is indicated on the accompanying diagram (Fig. 
609). 



The combination terminal heads are made in sizes to distribute an> 
number of cable conductors to line wires, from five pair to one hundied 
pair. The combination head is intended to be mounted in a metal outei 
case or pole box, to protect it rom the weather. In the accompanying 
drawing (Fig. 610) no attempt is made to show this outer case or the 
detail of the head, but it is the intention to show the manner of connecting 
up the cable wires and the convenient manner of forming the^ splice inside 
of the head. The covers are removed to show the wire splices. 

Reference to the suggested plan of cable distribution indicated in the 
diagram (Fig. 609), shows the greatest economy in the use of cables, as 
































































510 


TELEPHONOLOGY 


each cable contains exactly the number of wires required, leading to the 
various points of distribution, without waste or dead wires. The heads 
are designed to contain a small quantity of sealing compound, covering 
the ends of the cable sheaths, as in the junction box. This, with the coyer 
and rubber gasket, forms a double seal. This plan of cable distribution 
and use of the apparatus designed to eliminate sleeve splices and wipe 
joints has been in practical use for several years, and the firm 
manufacturing it states that fully one-half of its extensive orders for pole 
terminal apparatus for the past year have been for terminals of the com¬ 
bination type. 


25P * i*QAaa 


2Q0PAIR CABLf tOO PA/R CAdU 

OIRECT DISTRIBUTION 


SQPAiRQiaif OtDUM 


it 




IQQPA'A CAdlt MfW UH( 

RE-CONSTRUCTED ONE 


D 


t 


n- 


fl” 0 


2 5 PAtR CAAtJ 



DIRECT DISTRIBUTION- 


0 


20 PA/A 

IQ PAIR BCIRGII m/i Opt/ 
WITH *•! 


i_0“ (p™ n 

[ 4n ™ , r \ ' ' ■ ’ 


73PAIR CAQL[ 40PAIR CA3l£ 

yULTlPLE DISTRIBUTION 


2SP4/0 

IOPAIRI0 

n/uinpit 

WITH AT 2 


Fig. 609. 


The combination head is mounted in the Moon Metal Outer Case or 
pole box, and as the cover slides either above or below the head in open¬ 
ing, it can be placed just below a circular distributing frame, or below 
cross-arms. 

Multiple Cable Distribution .—It is the aim in modern telephone con¬ 
struction, to build permanently, providing as far as possible for increas¬ 
ing the capacity without abandoning or destroying work previously per¬ 
formed. Multiple cable distribution affords a certain amount of expan¬ 
sion by enabling one line to be used at two or more distributing points. 
As its name implies, the multiple method of cable distribution requires 
that the same pairs appear at two or more terminals. Since it is not 
always desirable or practical to complete the cable installation at its 
initial stage of construction, a method that will allow extra cables to be 
installed, without additional cost for terminals or changing present con¬ 
ditions is herewith described. 

Fig. 610 shows cable conductor, A, not only connected to line wire 
A, through the terminal head, but it extends from the terminal connec¬ 
tion, through conductor A in the continuing cable, to the next terminal 
head. 

The cut also shows conductor B spliced inside of the terminal head 
to the conductor, B, of the continuing cable, passing direct to the next 
distributing point. 

In this same manner, in Fig. 611, terminals 1 and 2 are connected in 
multiple, and to the exchange, by a fifty-pair cable. When desired, a 
new cable can be run from the exchange to terminal No. 1, and the cir¬ 
cuits at that point rearranged, giving full capacity to both terminals. 



















LINE AND CABLE CONSTRUCTION 


511 


A junction box can be used to great advantage when temporary mul¬ 
tiple distribution is desired, as shown in Fig. 612. The exchange cable, A 
is at first connected in multiple with the two cables B and C, the circuits 
of which being distributed at various points to subscribers’ stations, 
through permanent terminals. When the full capacity of cable B or C 
is required, an additional cable, D, may be extended from the exchange to 
the junction box, entering through an opening previously provided, or a 
200-pair cable may take the place of cable A (See Fig. 613). If a 200- 
pair cable is contemplated, a suitable opening in the junction box should 
be provided. These openings should be standard pipe tap, and then bush¬ 
ings can be used. The splices in the junction boxes are arranged as 
shown in Fig. 607. The obvious advantage of first extending the cables in 
multiple, and later increasing the capacity by using junction boxes, is 
apparent, as none of the original terminal work need be disturbed. The 
cable, B, shown vertical in Figs. 612 and 613, can, of course, be extended 
in any direction; it is so drawn in the illustration to clearly indicate its 
purpose. 



Tapping out wires from a junction box may be easily done at any 
time, if an opening for an additional nozzle is provided. A short piece of 
cable extends from the nozzle of the junction box to the nozzle of a termi¬ 
nal head, which may be located on the same pole (See Fig. 614.) 

The cable may terminate or dead end in the junction box, but the 
box should be provided with one or more additional openings for nozzles 
of proper size. 

Directions for making the cable joint with the Moon Self-Soldering 
Nozzle. j 

The terminal head or junction box is first fastened in place upon the 
pole. It is necessary to have the nozzle in a vertical position when the 
cable joint is formed. 

Before passing the cable end into the nozzle, remove a portion of the 
lead casing of the cable, leaving the cable wires free on the inside of the 
terminal head or junction box, so that they may be connected to the 
terminal connections on the inside of the head, or may be spliced onto 
other cable wires entering the head or box. Bind these wires with cord 
to prevent spreading. 




























































512 


TELEPHONOLOGY 


Mark off on the lead sheath of the cable the place that would come 
inside of the nozzle where the joint is to be made. 

Scrape the lead sheath at that point until it is bright and clean, then 
rub the bright or clean space with a tallow candle, soldering paste, or 
non-corrosive flux, which will cause the solder to unite with the sheath 
of the cable very readily when the solder is heated. The inner surface at 
the lower end of the nozzle is properly tinned before it leaves the factor}''. 

When the work of preparing the cable has been performed, pass 
the end of the cable up through the nozzle into the box. The lead sheath 
of the cables should extend into the box about one-half inch. 

Take ordinary insulating or adhesive tape and make a few turns 
around the lower end of the nozzle, lapping down onto the cable sheath, 
as is shown in the adjoining cut. This tape prevents the solder from 
running out of the nozzle when the solder melts. 


•front 


Box with self-soldering nozzle. Sectional 

Fig. 615. Fig. 615a. 

A litttle pulverized rosin sprinkled into the opening between the 
sheath of the cable and the nozzle after the cable is in place, will aid in 
the union of the metals. 

Then apply the blow torch to the nozzle below the terminal head or 
box, and heat the nozzle uniformly to a degree which will cause the sleeve 
of solder in the nozzle to melt and run down to a lower level, forming a 
union with the cable sheath and with the inside of the nozzle. 

To ascertain the proper heat, occasionally touch the outside of the 
nozzle with a piece of slender solder, similar to string solder, and when 
the nozzle is warm enough to melt the solder on the outside, it is evident 
that the solder contained in the nozzle has melted and has formed the 
joint. 

Continue the heat on the nozzle for one half minute or so, to give the 
solder ample time to form a thorough union. Then cool the nozzle with 
a wet piece of waste or rag, and remove the tape, and it will be found 
that a perfect cable joint has been made. 




new of nozzle. 























LINE AND CABLE CONSTRUCTION 


513 


After connecting up the cable wires, or making the splices in the 
manner indicated in the accompanying cuts, pour a quantity of paraffine 
or cable compound into the pocket or cavity at the lower end of the box. 
This compound will surround the cable wires, cover the end of the cable 
sheath and will fill the cavity in the nozzle above the solder, forming an 
additional seal, and prevent injury to the cable when the box is opened 
for any purpose. 

To close the terminal head or junction box after all connections are 
made, first see that the rubber gasket forming the cover joint, is in proper 
place. Then screw on the cover, setting screws in snugly. Remove 
screw plug at top of box, and with the blow torch slightly warm the cov¬ 
er of box. This will evaporate all the moisture from the air in the box, 
allowing it to discharge through the opening at the top of the box. 

While the cover is still warm, again set up the screws of cover snug¬ 
ly. Then replace the screw plug at top of box. This partially forms a 
vacuum in the box, which is perfectly free from mositure. 

If the box is ever opened, repeat process. 

Where the junction box is intended for use in a manhole it should be 
specified in ordering, as they differ in some particulars from those used 
on poles. 



Fig. 616. 


*“In offices where one man has to do everything without the assist¬ 
ance of another the duties sometimes include the picking of pairs in a 
new cable. The writer suggests a method that has been used by many 
under the circumstances, but which, however, may be new to some of our 
readers.” 

“First, fan out the office end of the cable and connect it to the rack at 
random, being sure that the red and white components of a pair are in 
regular order on the rack. Open the other end of the cab:e—but only 
when the air is free of moisture—and test for “bad” pairs at the office 
end.” 

“This can be done by using the contrivance shown in Fig. 616, which 
consists of a receiver, two cells of battery and a pick . A convenient 
“pick” can be made from a large needle, such as is used in sewing burlap 

sacks.” 

“To test for “grounded” pairs, connect the receiver to the sheathing, 
as at G, and run over the terminal, or rack, connections with the pick. In 
case any conductors are “grounded’ on the sheathing, a click will be 
heard in the receiver, due to current flowing from the batteiy, thiougn 


*American Telephone Journal. 
33 






















514 


TELEPHONOLOGY 


the pick and faulty wire to the sheathing, and back to the receiver. Any 
“bad” pairs thus located should be set aside and tagged as such. Fig. 617 
shows method of connecting to locate grounded pairs, or conductors. 
“Open” conductors or “crosses” cannot be located in this way, though 
crosses may be by using a second pick in place of G and testing each pair 
separately, and each pair with every other pair.” 

“Assuming the new cable tests clear, as it should, connect the “red” 
side of pair one, as in Fig. 617, in the office to G on the cable sheathing, 
through a battery. Then connect the white side of the same pair—pair 
one—to the “red” side of pair three, and so on down the rack. Always 
connect the “white” side of a pair to the “red” side of the succeeding pair, 
in regular order, so that the “white” side of the last pair has nothing to be 
connected to.” 

“Now go out on the terminal, with your locating contrivance (Fig. 
616) and attach the battery to the cable sheathing. Touch each of the 
exposed “red” conductors with your pick till you get “battery”, or a click 
in the head-receiver. As there is only one conductor in the cable that has 
“battery” on it, and that is the “red” side of pair one, you can safely tag 
the “red” wire and its “white” component as “pair one.” 




“Now attach the “white” wire of pair one to the “red” (battery) 
wire of the same pair, and pick over the “red” conductors again. When 
you get* “battery”’ again, you know you have found the “red side of pair 
two, for the battery current from the “red” side of pair one flowing back 
to the central office rack over the “white” side of pair one, and comes out 
to you again on the “red” side of pair two. You have the “white” side of 
pair two twisted with the “red” side, so no further identification is neces¬ 
sary. Tag this “pair two.” ” 

“Now disconnect the “white” side of pair one from its “red” mate— 
the battery wire—and attach the “white” of pair two to the “red” battery 
wire of pair one. Go over the untagged pairs until you get “battery” 
again, which will, of course, be on the “red” side of pair three. Tag it as 
such, attach its “white” mate to the “battery wire” of pair one and locate 























































LINE AND CABLE CONSTRUCTION 515 

vou r have'u y0U l0Cate the “ red ” side of the Iast P air 
you have its white mate without need of further identification.” 

to twpritv y( + U ^ aV f G a ?^'P a ^ r cable, and wish to take out pairs one 

inothPr W fhi °£n termm ^~ as a top-and pairs twenty-six to fifty at 
another box, the following idea may prove available: 

Connect every “red” and “white” wire together, from one to twenty- 
five, as a solid conductor, Fig. 618. From the “white” side of pair twenty- 
five run the connecting wire to G on the cable sheath through a batterv 


Then go to the point on the cable where it is desired to tap these 
wenty-five pairs, and lay open the sheathing. Touch each conductor with 
your pick it will go through the paper covering—and tag every wire on 
which you get battery.” That will locate the first twenty-five pairs. 
1 hen go to the other point, where the pairs twenty-six to fifty are desired, 
and tag every pair upon which you do not get “battery”. The number of 
each pair can be ascertained later by the method described. Multiple 
taps can be made in the same method, by putting “battery” on such pairs 
as you wish to appear at certain points. Ordinary dry cells will give 
results in all these cases, but “tone test” is better. It is a noise that will 
work through almost any resistance, and cannot be mistaken when heard. 
An apparatus for giving “tone test” can be arranged very easily as fol¬ 
lows :” 



“An ordinary “buzzer” or electric bell with the gong removed is con¬ 
nected to a couple of cells of battery (Fig. 619). Connect a wire to the 
make-and-break screw, C, and another to the armature spring, P, or the 
frame of the bell. (One side of the battery will do as well, providing you 
get right side.) Ground the wire from C through an ordinary condenser, 
as at G. The other wire take to the head-phone and out to the pick. 
When the pick strikes a grounded wire, or completes the circuit to G in 
any way, a peculiar buzzing noise is manifest in the receiver or head¬ 
phone. It can never be mistaken when once heard, and is particularly 
serviceable when there are “working wires” in a cable, that is, subscrib¬ 
er’s circuits. The condenser prevents any signals being thrown on the 
board, and seems to take the “rough edges” off the noise itself.” 

“The loudness of the “tone” can be regulated by the tension of the 
armature spring.” 

“It can be used to take the place of the ordinary battery “click” in 


























516 


TELEPHONOLOGY 


the location and selection methods described in this article, and will find 
favor at once.” 

“Buzzer, battery and condenser can be mounted together as one piece 
of apparatus, and one-point switch included to start the buzzer. With two 
cells of ordinary dry battery it will run for hours without attention, the 
writer having had one running twenty hours continuously without ex¬ 
hausting the batteries to any extent.” 

“In making the test for pairs the two batteries should be in series. 
Otherwise the click might be too faint to test with; or else the battery of 
the test set should be disconnected from the circuit.” 


/ 


CHAPTER XIV. 


THE AUTOMATIC TELEPHONE SYSTEM. 


By far the best known and most widely used of the various automatic 
systems is that manufactured by the Automatic Electric Company, Chi¬ 
cago, and known as the Strowger Automatic, or more commonly as the 
“Automatic.” 

The first patents on this system were issued in 1890 to Almon B. 
Strowger. In 1892 Mr. Alexander E. Keith, at present General Super¬ 
intendent and Chief Engineer of the Automatic Electric Company, as¬ 
sumed charge of the work of development and under his direction the first 
exchange was manufactured and installed at La Porte, Indiana. 

It is principally due to the untiring efforts of Mr. Keith that the sys¬ 
tem has reached its present high state of perfection. 

The La Porte exchange was necessarily crude in form, and required 
four wires between the subscriber’s station and the exchange, besides a 
common return, but it demonstrated that the automatic system was 
possible. 



Fig. 620. Common Battery An- Fig'. 621. Automatic Desk Teie- 

tomatic wall Telephone. phone. 

In 1894 Messrs. Chas. J. and John Erickson, two inventors of unusual 
abilitv became associated with the Strowger Company and in the fall of 
the same year a new switchboard of one hundred (100) line capacity was 

(517) 












518 


TELEPHONOLOGY 


installed at La Porte, Indiana, replacing the older one, and reducing the 
number of lines per subscriber to two and a common. 

In 1895 the vertical and rotary type of switch was developed and a 
number of installations of 200 lines capacity were. made. 

The trunking feature was first used in 1897 when an exchange of 
one thousand lines capacity was installed at Augusta, Georgia. Two 
years later, in 1899, the automatic trunking system was perfected and an 
exchange of 10,000 lines capacity was installed at New Bed ord, Mass. 
This exchange is still in operation. The Automatic selection of trunks 
solved the problem of the capacity of the automatic switchboard and since 
its introduction, the growth and development of the system has been very 
rapid. Several exchanges of 100,000 lines capacity are now in operation 
and in certain instances of trunking between exchanges the 1,000,000 
system is employed. 

A description of the types of the apparatus used during the different 
stages of development of the system would be of interest to the student of 
telephony, but as it is not possible to treat the subject fully within the 
limits of this article, we shall confine ourselves to the exposition of the 
exchange equipment as manufactured and operated today. 

In the automatic system the subscriber’s station is connected to the 
exchange by two line wires designated respectively “vertical” and “ro¬ 
tary”. By operating the dial of the telephone, the vertical line is ground¬ 
ed a number of times, corresponding to the figure from which the dial is 
rotated. The rotary line is automatically grounded once after each series 
of vertical impulses. Thus, in calling 7256 for example, current impuls:s 
are transmitted to the exchange as follows: Seven vertical, one rotary; 
two vertical, one rotary; five vertical, one rotary; six vertical, one rotary. 
In addition, a preliminary impulse is made automatically on the rotary line 
as the dial is being pulled down for the first digit. 

When the call is completed and the ringing button depressed the vertical 
line is again grounded. When the switch hook is pulled down, as in 
hanging up the receiver after making a call, both vertical and rotary lines 
are grounded momentarily at the same time. 

At the exchange the line terminates in a line switch and also in a pair 
of contacts which are multiplied throughout the banks of a group of ten 
connectors. 100 pairs of contacts comprise a connector line bank, being 
arranged in ten parallel rows of ten pairs of contacts each. By operating 
a connector shaft five steps vertically and then rotating it six steps, 
for instance, a connection is established through the contact arms or 
wipers of the connector with contact number 56 in the bank, which is line 
number 56. If the number to which the connector be rotated is busy, the 
switch will be automatically released and the busy signal thrown on the 
calling line. The automatic release from a busy contact is effected 
through the busy or private bank which comprises single contacts multi¬ 
plied throughout the ten connectors in the same manner as the line banks. 

If a line be connected directly to a connector, the connector is opera¬ 
ted by the ground impulses at the telephone. Since in actual practice it 
rarely occurs that more than ten lines in any group of one hundred in an 
exchange are being called at the same time, the 10 connectors are suffi¬ 
cient to establish all connections to 100 subscribers, but it is necessary to 
provide means for enabling the calling line to secure anyone of these ten 
connectors. 







Fig. 622. Line Switch Unit. (Front view.) 


519 

















520 






















Fig. 624. 


Line Switch Unit. (Rear view.) 


521 















Fig. 625. Shelf of Connectors. 


522 
































THE AUTOMATIC TELEPHONE SYSTEM 


523 


In the 100 systems or two-figure system, the function of the line 
switch, to which each line is directly connected, is to automatically switch 
the line of the calling subscriber to an idle connector. This is accom¬ 
plished through the banks of the line switch which comprise ten pairs of 
contacts or jacks multipled throughout the entire 100 line switches and 
wired directly to the connectors. These connecting lines are called trunks. 

The ten pairs of bank contacts in any line switch are paralleled by two 
common strips of contacts or jack springs connected to the line itself. 
The line switch has a plunger or a plug which effects the connection from 
the line to a trunk by closing these contacts, the action being analagous to 
inserting a plug in a jack in the manual switchboard. 

The plungers of all the 100 line switches in the group normally en¬ 
gage with a common shaft and are pivoted in such a manner that when the 
shaft is rotated, the plungers are carried from one to another of the ten 
trunks but without making contact, the plungers being simply poised in 
front o the contacts. The common shaft is rotated by a simple mechan¬ 
ism called a master switch. If, while the plungers are all held by the 
shaft directly in front of contact or trunk No. 1, a subscriber begins a call, 
his line switch plunger, by the preliminary impulse, will be automatically 
“tripped” in on this trunk, disengaging from the shaft. Besides closing 
the calling line through to connector No. 1, the plunger also closes a local cir¬ 
cuit which actuates the common master switch, rotating the shaft one step, 
thus removing all remaining 99 plungers to trung No. 2. Another subscriber 
beginning a call will now occupy trunk No. 2, moving the remaining plun¬ 
gers to trunk No. 3, etc. When all ten trunks have been occupied in suc¬ 
cession, the shaft rotates back to trunk No. 9, then to trunk No. 8, etc, 
until finally the plungers are again in front of trunk No. 1 and the cycle is 
repeated. The rotation never proceeds more than one step unless the 
trunk to which the plungers are directed is occupied, in which case the 
shaft is automatically rotated another step, etc. If all ten trunks are 
occupied, the shaft will continue to rotate until a trunk is freed. 

The 1,000 or three figure system comprises ten groups, or units, each 
consisting of 100 line switches and ten connectors as described. In order 
that the different groups may be intercommunicating, another series of 
switches, called selectors, is introduced, and the trunks from the line 
switch banks instead of leading to connector switches, are brought to 
these selectors. The function of the line switch is now to connect the 
calling subscriber’s line with an idle selector, and the function of the selec¬ 
tor is"to further connect the line with an idle connector in the hundred 
group into which it is desired to call. 

The blanks of the selectors comprise one hundred pairs of contacts, 
arranged in ten rows the same as the connector banks, and multipled 
throughout the entire one hundred selector switches, the first row or level 
of contacts being continued to the fen connectors in the 100 group the 
second row to the ten connectors to the “200’ group, etc. 

In calling number 256, for example the line switch plunger of the call¬ 
ing subscriber is automatically tripped in on a trunk to a selector. The 
two impulses on the vertical line step the selector shaft up to the second 
row or level of contacts, the single rotary impulse starting it rotating over 
the contacts. It will rotate one step, stopping the wipers on the first con¬ 
tacts which is the first connector in the 200 group, provided none of the 
other 99 selectors are occupying that contact, in which case the shaft auto¬ 
matically rotates to the second contact, etc., not stopping in its rotation until 


524 


TELEPHONOLOGY 


it has found a contact, that is, a connector which is not in use. The line 
of the calling subscriber now being connected through to a connector in the 
group desired, the two remaining digits of the number operate the connec¬ 
tor shaft vertically, and then rotate it to contact 56. The automatic selec¬ 
tion of an idle contact or trunk line by the selector is controlled by the 
private bank which comprises single contacts multipled in the same manner 
as the line banks. 

The 10,000 of four-figure system comprises ten 1,000 systems or 
groups as described. To effect the interconnection among the different 
thousands, another series of selectors is introduced, and the trunks from 
the line switch banks are brought to these switches, which are called first 
selectors to distinguish them from the selectors of the thousand groups 
which are now called 2nd selectors. The function of the line switch, as 

in the 1,000 system is to connect the calling subscriber’s line with a first 
selector. The first selector further connects the line with a 2nd selector 
in the thousand group desired, and the 2nd selector still further connects 
the line to a connector in the particular hundred group into which it is 
desired to call. The bank contacts of the first selectors in each of the ten 
groups are multipled throughout the 100 1st selector switches, and are 
continued to second selectors, the first row or level of contacts being con¬ 
nected to ten second selector switches in the “2,000” group, the third to 
the “3,000” group, etc. This arrangement provides 1,000 second selectors 
through which calls may be made or 100 for each thousand group. 

In calling 7256 for example, the line switch plunger is automatically 
tripped in on a trunk to a first selector. The seven vertical impulses step 
the first selector shaft up to the seventh level of contacts, the single rotary 
impulse starting the rotation by which the first free contact in the row is 
automatically selected. The calling line is now connected to a second selec¬ 
tor in the seventh thousand group, and when the next digit, 2, is called, a 
connector in the “200” group of this thousand is automatically selected as 
described in the 1,000 system, the last two digits being made on the con¬ 
nector. 

The 100,000 or five figure system comprises ten 10,000 systems or 
groups. To effect the inter-connections among these ten groups, another 
series of switches called 3rd selectors is introduced, the selection of 
trunks and the operation of the switches being substantially as described 
for the 10,000 system. 

The automatic is strictly a trunking system and the automatic selec¬ 
tion of trunks makes it possible to construct exchanges of any capacity, 
or to subdivide an exchange in almost any manner desired without affecting 
the operation. The 1,000 system may be used in combination with the 10,- 
000, the 10,000 with the 100,000, etc. Whatever system or combination 
of systems be employed, the object is the same, viz: the ultimate selection, 
through trunks, of a connector, the banks of which contain the line con¬ 
tacts of the desired subscriber. 

While it has been convenient to describe the system as having 10 
per cent, trunking capacity and while this is ordinarily sufficient, it should 
not be inferred that the system is limited to any particular percentage. 
In some instances of busy sections as high as 20 per cent, is employed. 
Any desired percentage may be provided by the proper arrangement of 
the interconnecting switchboard wiring, without changing switches or 
banks in any particular. 


525 


THE AUTOMATIC TELEPHONE SYSTEM 

Thus, the 100 line switches belonging to a particular group are di¬ 
vided into two sections each controlled by a separate master switch. 
Ordinarily the trunks from both sections are multipled together at the 
terminal strip, but if these trunks be brought separately to first selectors, 
the outgoing trunk capacity will be thereby increased to 20 per cent. 

To provide increased incoming trunking capacity into any particular 
hundred group it is only necessary to open the selector bank multiples at 
the proper terminal strip and wire each section separately to connectors. 
For this purpose each hundred group or unit is provided with space for 
additional connectors. Increased trunking capacity between the different 
thousand groups, or between different exchanges is accomplished in the 
same general manner, there being practically no limit to the different 
trunking arrangements which may be made. 

Since any automatic exchange consists of a number of groups of units 
with interconnecting trunks, it will readily be seen that the sub-division of 
a plant into a number of branches presents no problems. The exchange is 
already sub-divided. It is only necessary to fix the location of the branches 
or units which compose it. 

If we consider two exchanges, A and B, of 1000 lines each, the lines 
in exchange A for instance, will be numbered from 1000 to 1999 and the 
lines in exchange B from 2000 to 2999. In A exchange, the trunks from 
the second row or level of multiplied bank contacts of the first selectors are 
continued to second selectors in exchange B, so that any subscriber calling 
2 for the first figure will step a first selector up to the second level of 
contacts and automatically select an idle trunk terminating in a second 
selector in exchange B, where the call is completed. In exchange B, the 
first row or level of the first selector bank contacts is continued to second 
selectors in exchange A, and any subscriber calling 1 for the first figure 
similarly secures a second selector in exchange A. 

For convenience, the dials of the telephones are sometimes lettered as 
well as numbered and a certain line in exchange B may be designated, for 
instance, as B-756 instead of 2756, the two being, of course, identical. 

Ten such exchanges may be interconnected, each being designated 
by a different figure or letter, and the selection and operation proceeding 
exactly as when the switches are all in the same exchange. 

The exchanges are not limited as to capacity. Each may have 10,000 
instead of 1,000 lines, and any or all of the component exchanges may be 
further sub-divided into two or more branches, if desired. 

Fig. 626 shows a plan of the six interconnecting automatic exchanges 
serving the city of Los Angeles, Cal., three of these being further sub¬ 
divided, making eight exchanges in all, the two farthest being over 13 
miles apart. 

The automatic system is peculiarly adapted for sub-divided exchanges, 
because a call is made as quickly and as accurately through two or more 
exchanges as through a single exchange, and because the cost of operation 
and maintenance is not materially increased by reason of the sub-division. 
It possesses an added advantage of great importance, in that the number 
of interconnecting trunks required is considerably less than in case of a 
manual system as shown by actual statistics. The reason for this is ap¬ 
parent when it is considered that in an automatic exchange of 100,000 
capacity, the average time elapsing from the instant of beginning a call 
until the called subscriber answers is 18 seconds, while in the largest and 


526 


TELE PHONOLOGY 


best equipped manual exchange, this time is 30.39 seconds for a connection 
in the same office, and 35.89 seconds for a trunked connection through two 
offices. If the disconnect be included, the operating time is increased to 
18.50 seconds for the automatic and 38.99 for the manual. The difference, 
20.47 seconds, represents the saving in time effected by the automatic. If 
the average time of conversation one minute and twenty seconds in each 
case be included, it will be seen that the saving in time during which a 
trunk is occupied per connection is approximately 17 per cent. 



The distinguishing features of the automatic telephone is the impulse 
sending mechanism, or calling device consisting of the dial and its ac¬ 
companying mechanism. 

All other parts, transmitter, receiver, induction coil, ringers, condenser 
and switchhook are of the usual type and require no description. 

The dial is on the front of the instrument, in the most convenient 
position for operating, and is secured directly to the shaft of the calling 
device which is inside of the telephone box or case. It consists of a revolv¬ 
ing wheel or disc about four inches in diameter provided with ten finger 
holes arranged on its periphery and numbered from 1 to 0, beginning at 
the bottom. The finger holes are on the right side of the dial and occupy 
less than half of its circumference. In calling 256, for example, the sub¬ 
scriber removes the receiver from the hook, places his finger in the num¬ 
ber 2 hole and pulls down the dial, rotating it until his finger comes in 
contact with a stop. Upon removing the finger, the dial immediately ro¬ 
tates back to its normal position. The subscriber then pulls down the 5, 
and then the 6, completing the connection with the called party, and sig¬ 
nals by pressing the ringing button. 

The essential part of the calling mechanism is the impulse wheel 
which is attached to the dial shaft and which rotates with it. This im¬ 
pulse wheel has ten teeth which correspond to the 10 finger holes in the 













527 


THE AUTOMATIC TELEPHONE SYSTEM 

dial, and which engage with the vertical impulse spring upon the return 
movement of the dial. An extra single tooth also engages with the rotary 
impulse spring. The dial is brought back to normal position after each 



Fig. 627. Wall phone and hand showing method of operation. 


rotation by a strong clock spring which is attached to the dial shaft. A 
small centrifugal governor geared to the shaft by a one to twenty gear, 
regulates the rate of speed of the impulse wheel. 






Szss ss-t g <• CiTf 



Fig. 628. Circuit Common Battery Wall Phone. 





















































































































528 


TELEPHONOLOGY 


Fig. 628 shows the circuit and mechanism of the telephone. When the 
receiver is on the hook the ringers and condenser are bridged across the 
line, and the dial locked in position. Upon removing the receiver the tele¬ 
phone is in the talking position with transmitter and primary of the 
induction coil across the line, the receiver being included in circuit with 
the secondary of the induction coil. 

When the dial is pulled down, the ground spring is closed and the 
connection between the two lines through the transmitter is broken. In 
this position, the lines end in the impulse springs and as the dial returns 
to normal, the teeth of the impulse wheel slide over the vertical spring in 
such a manner as to press it against the ground contact a number of times 
corresponding to the figure which has been pulled down. Following these 
vertical impulses the extra impulse tooth slides over the rotary spring 
pressing it against the ground spring once. 

The talking circuit is broken each time the dial is pulled down and 
closed as soon as it has returned to normal. When the subscriber pushes 
his ringing button, the talking circuit is again opened and the vertical line 
grounded as long as the button is pressed. 

When the receiver is restored to the switch hook or when the hook 
is pulled down, the three release springs are pressed together momentarily 
grounding both vertical and rotary lines at the same time, which action 
always releases the switches in the exchange. Should the hook be moved 
up and down before rotating the dial, however, no release action takes 
place as the ground spring is not closed. 

The dial may be pulled down as fast or as slowly as desired, since the 
governor engages the shaft only on the return movement. The switches 
in the exchange will operate successfully at any desired speed up to about 
18 impulses per second, the governor usually being adjusted so that the 
vertical line is grounded at the rate of 12 to 15 times per second. 

The time required to make a call depends, *of course, on the size of 
the number and the speed of the operator, the average for a four-finger 
number being being 3 to 7 seconds. 

In describing the operation of the switches, it is not the purpose to 
enter into detailed description of mechanical construction further than is 
required for a clear understanding of the essential features. The com¬ 
mon battery system only will be described, as this represents the latest in 
automatic practice. 

The line switch, selector and connector will be described in the inverse 
order of their operation. 

Fig. 630 represents a common battery connector in combination with 
its electrical circuits. The switch is operated by ground impulses imparted 
at the telephone of the subscriber and directed to the two relay electro¬ 
magnates VR and RR, called respectively vertical and rotary relays, which 
are bridged across the line at the exchange. These relays operate two 
springs, SI and S2, which take up the ground impulses and direct them to 
different parts of the switch. 

The only mechanism which undergoes translation and rotation is the 
shaft A situated in front of the switch. The middle o" the shaft contains 
a hub, H, the upper half of which is milled to form ten horizontal circular 
teeth, and the lower half longitudinal teeth. These are engaged respectively 
by the pawls PI and P2 on the vertical and rotary armatures VA and RA, 
when these are acted upon by the vertical and rotary magnets V and R, 





Fig. 629. 


Connector Switch. 

529 


34 













530 


TELEPHONOLOGY 


magnet rotates the shaft one step, each step corresponding to one of the 
ten contacts in the bank row. After each vertical impulse the shaft is 



7 


Fig. 630. Circuit and mechanism of Connector Switch. 

vertical magnet raises the shaft one step, each step corresponding to a 
certain level or row of bank contacts. Each impulse through the rotary 


iHHHilii 





































































































































































































THE AUTOMATIC TELEPHONE SYSTEM 


531 


enabling the shaft to be raised and rotated. Each impulse energizing the 
retained in position by the upper tooth Tl, of the double dog DD the lower 
tooth of which T2, performs the same office for the shaft after rotation. 
This rotation may occur at any one of the ten vertical positions the shaft 
being supported by the fixed dog F D. The lower part of the shaft holds 
the line and private wipers, the top, or private wiper P W, operating on 
the private banks, forming the release trunk, while the lower or line 
wipers V W and R W connect the vertical and rotary lines with the cor¬ 
responding contacts on the line banks. These wipers which are rigidly 
attached to the shaft, form the jaws of a knife switch which engage the 
bank contacts. 

The impulses, repeated by the vertical and rotary relays, are directed 
to various parts of the switch by the action of the side-switch. The side- 
switch in this case consists of four knife switches, a, b, c and d insulated 
from one another and mounted upon a shaft rigidly attached to the end of 
the spider arm S A pivoted at B and operated by a spring at C. The 
action of the spider arm is controlled by a finger F engaged by two escape¬ 
ment springs E S fastened to an arm of the private armature P A. In the 
normal position of the switch the finger F of SA is in the position shown. 
An impulse through the private magnet P M pulls down the private arma¬ 
ture, allowing F to fall against the upper tooth of E S. Upon cessation 
of the impulse, the armature assumes the normal position and F passes 
into the second place of the lower escapement spring, the spider arm car¬ 
rying the side switch into the second of three positions 1, 2 and 3. Upon 
the next impulse through the private magnet, F is carried out against the 
stop X, and the side-switch takes the third position. 

Battery is thrown upon the vertical line V L through the vertical 
relay V R in series with an additional coil Yl. Similarly, the rotary line 
R L receives battery through the relay R R in series with the coil Y2. 
The two coils Yl, Y2 one above the other, are differentially wound on the 
same core and an impulse over either line will actuate the armature Y A. 

The two line relay armatures when attracted by the relay magnets 
V R and R R, throw ground respectively on springs S 1 and S 2. Spring 
S 1 when closed, forms part of a circuit passing through the spring con¬ 
tact of the private relay arm P A, and the side switch (a), and the coils 
of the vertical magnet V to battery. Spring S 2 closes the circuit through 
the private magnet P M and springs S 3 to battery. 

By the construction of the telephone, every series of impulses over 
the vertical line is followed by one impulse over the rotary line without a 
special act of the subscriber. A series o ' impulses over the vertical line is 
transformed into an equal number of vertical steps imparted to the shaft 
by the attraction of the vertical armature V A to the vertical magnet V. 
The succeeding impulse over the rotary line allows the side switch (a) 
to pass into position 2. 

The next series of impulses over the vertical line will be transformed 
into an equal number of steps imparted to the rotary shaft by the action of 
the rotary armature R A. Again the impulse over the rotary line, operat¬ 
ing the private magnet, allows the side switch (a) to occupy position 3. 
It will now be seen that the vertical and rotary lines are connected through 
the side switches (c) and (d) to the wipers M W and R W and that the 
private wiper P W is connected to ground through side switch (b). An 
impulse over the vertical line will now throw ground through position 3 of 
side switch (a) upon the ringer relay G R, which acting upon a pair of 


532 TELEPHONOLOGY 

springs throws an alternating current from the generator upon the called 
lines. 

When the called subscriber takes his receiver from the hook, a circuit 
is closed through the receiver over the vertical line to main battery through 
coil Zl, and to ground over the rotary line through coil Z2, thus supplying 
current for talking to the called line. Coils Zl and Z2 mounted in a 
like manner as Y1 and Y2, but with their magnetic forces acting in the same 
direction attract armature Z A thereby throwing the rotary line of the 
calling subscriber by the action of spring S 3 from battery to ground. 
Since the receiver of the calling subscriber is removed from the hook, a 
circuit is then completed from the ground at side switch (b) through coils 
Y2 and R R, over the calling line, back through coils V R and Y 1, to main 
battery, thus supplying current to the other half: of the line. Relays V R 
and R R may or may not be operated by this current, but coils Y1 and Y2, 
now in series, have their magnetic forces opposed so that armature Y A is 
not attracted. Connections between the calling and called lines is made 
through condensers Cl and Dl, of two microfarads capacity each. 

Upon completing the conversation, the switch is released and restored 
to normal in the following manner: A ground impulse imparted simul¬ 
taneously to the vertical and rotary lines, upon hanging up the receiver, 
actuates the differential relay by shunting out the circuit of coil Y2. This 
relay throws main battery on one side of the release magnet Rel M, at the 
same time opening the circuit of the relay Z, which in falling back re¬ 
stores the rotary line of the calling subscriber to main battery. Both V R 
and R R are operated by the release impulse at the telephone, thus closing 
the front release springs S4 and S5. Spring S4 is grounded through a 
half ohm coil of a selector over the release trunk Rel T. and spring S5 is 
connected directly to the release magnet which attracting its armature 
causes the double dog to release its clutch on the shaft. A release link Rel 
L, dropping over a finger of D D retains it until the switch is again used. 
The shaft on being released by D D, is rotated back by the tension of a 
coiled spring C S until it is stopped by the finger S F striking the normal 
post N O, when it is dropped to its original position. The same motion 
which withdraws the double dog also restores the arm S A by means of the 
finger D F acting through a link S L upon the lever SAL. When the switch 
is next used the first vertical impulse raises the release link by means of the 
finger V A F on the vertical armature, allowing the double dog to be acted 
upon by a spring which returns it to the shaft. The switch can thus be 
released from any position. 

Connection with a busy line is prevented by an automatic release of 
the connector, as follows: The private wiper of the connector throws 
ground on the private contact corresponding to the line contacts of the 
called subscriber, from side switch (b) in position 3. The last impulse 
over the vertical line of one subscriber who is making the same call as 
another, causes the private wiper of his connector to engage a multiple of 
the private bank contact occupied by the other subscriber while the side 
switch of the former is still in position 2. Consequently, the wiper P W 
receives ground from the side switch (b) of the latter connector through 
the private bank. 

The in'pulse over the rotary line which follow every series o" vertical 
impulses, as noted before, energizing private magnet P M, which in attract¬ 
ing armature P A closes springs S 6 and S 7, throwing main battery on the 
grounded private wiper through the release magnet, effecting the “busy” 


i 




THE AUTOMATIC TELEPHONE SYSTEM 533 

release. The subscriber, not yet knowing that his connector has been re¬ 
leased, grounds the vertical line in order to ring. The connector responds 
by raising the vertical shaft. The off normal springs 0 N which are held 
open by the finger S F when the switch is at normal now closes, connecting 
the rotary side of the line with the generator, which by an inductive 
effect, produces the common “busy” signal. 



Fig. 631. Diagammic circuit of busy release. 







































































































































































































































































































534 


TELEPHONOLOGY 


Fig. 631 shows diagrammatically how this release is effected. 01 is 
here represented as having called 05 whose normal leads are connected 



Fig. 632. Circuit and mechanism of Selector Switch. 


„ jj ij ii • 

with the fifth contact of the tenth bank level. 02 attempts to call 05 and 
engages a multiple at Z of the contact still occupied by 01, with his last 
































































































































Fig. 633. Individual line and switch bank. 


535 





























536 


TELEPHONOLOGY 


impulse over the vertical line while his side switch (b) is in the second 
position. The succeeding impulse over the rotary line causes the private 
armature to close two springs which complete the circuit through the re¬ 
lease magnet to battery. If instead of 05, 02 attempts to call 01, the 
release is similiarly accomplished. The normals of switch 01 are connect¬ 
ed to the first contact of the tenth bank level, and the shaft being off nor¬ 
mal, the off normal springs are closed, throwing ground over the private 
normal upon this contact. 02 upon engaging a multiple of the same con¬ 
tact has his connector released as before. 

Fig. 632 graphically represents the parts of a first selector with cir¬ 
cuits. The purpose of a selector being to select a trunk line only, it is more 
simple than the connector, and coils Y1 and Y2, Z1 and Z2 and G R do 
not appear. An additional coil B REL called the back release relay, and 
the interrupter springs 1 S, constitute the chief mechanical addition. 

The step by step rotary movement of the first selector is automatic 
and not operated by the subscriber. After the first series of impulses over 
the vertical line has raised the wipers to the desired level, the following 
impulse over the rotary line operates, as before, the private magnet P M. 
This magnet, attracting the private armature P A allows the finger of S A 
to pass directly from position 1 to position 3 in the following manner: 

When F, together with the side switch, passes into position 2 a circuit 
from ground at side switch (a) passes through springs L S and the rotary 
magnets R to battery. The rotary armature R A in pulling up presses 
down mechanically the private armature by means of the rotary armature 
finger RAF, allowing F to fall against the upper tooth of the escapement 
spring E S. At the same time the circuit through R is broken by means 
of the rotary armature finger L F which is interposed between the two 
interrupted springs. The circuit being broken, the rotary armature is 
pulled back by the action of a spring and the private armature rising, 
allows F to pass to position 3. The wipers are thus left by the one rotary 
impulse upon the first bank contact of the row to which they were carried 
by the vertical impulses. The two lines V L and R L are thereby connected 
directly with the first connector of the group, further operation of the first 
selector being prevented when the side switches C and D passed into 
position 3. The private wiper P W of this selector, now throws ground 
upon the private bank contact through the half-ohm coil B Rel, mentioned 
before as being connected with the front release spring S 4 of the connector 
over the release trunk Rel T. 

Another subscriber calling into the same group will obtain a second 
connector in the manner described herewith. At the first impulse over 
the rotary line the side switch B will pass into position 2 and the private 
wiper will engage the multiple of the contact previously grounded. The 
interrupter finger IF breaking the circuit through the rotary magnets 
allows the rotary armature to fall back. The private armature, however, 
remains held down due to the ground receiver by the private magnet 
through the wiper P W. The interrupter springs again closing the circuit, 
the shaft is rotated another step. The private wiper now resting on a 
contact not grounded, the private armature is released and the finger F 
passing into position 3 leaves the lines connected with connector 2. As 
long as the private wiper continues to engage a grounded contact, it will 
rotate automatically, the side switch being unable to pass out of position 
2 until the private armature is released. 


THE AUTOMATIC TELEPHONE SYSTEM 


537 


Owing to the fact that the first selector is entirely eliminated from 
the line circuit after the side switch reaches position 3, its release is 
effected by the connector over the release trunk Rel T. Rel T. of Fig 9 is 
connected with one of the 100 contacts of the first selector private banks 
P B, and from there with a ground through the back release coil B rel 
when the private wiper engages the contact. When the front release 
springs of the connector are closed during the release, the coil B rel, 
energized, attracts its armature and throws ground on the release magnet, 
thereby releasing the first selector. 


MASTER SWITCH 



Should the subscriber for any reason wish to release his first selector 
before obtaining his connector, he accomplishes this by grounding both 
the vertical and rotary lines. The rotary line energizing the private 
magnet causes spring S2 connected with release magnet Rel 1, to make 
contact with SI, now receiving ground from S which is grounded by the 

impulse over the vertical line through coil V R. .. , , 

The operation of the line switch has already been partially described. 
The circuits and mechanism are extremely simple, since the only movement 
required is to drop the plunger a distance o e three-eights of an inch into 
the bank jacks or contacts at the beginning of a call, and to restore it again 
at the end of the call. 









































































































































538 


TELEPHONOLOGY 


Fig. 634 represents (witch circuits) two adjacent line switches in the 
relative positions which they occupy when mounted, together with a 
graphical representation of the master switch, of which two are assigned 
to each line switchboard unit. Switch No. 1 is shown with plunger released 
from shaft and engaging trunk No. 6, while the plunger of switch No. 2 
is in a position to take trunk No. 7 upon the next call. 

These plungers are directed to the proper contacts by the operation 
of the master switch upon the two shafts located centrally in front of 
their respective panels. The two shafts are operated by one master 
switch (the second master switch being a reserve only) sufficiently at each 
call to direct all the plungers not released to the next multiple bank 
contacts. 

The wheel of the master switch has a forward movement only and 
operates the shaft mechanically by an arm reaching from the rim of the 
wheel to the point where its axis of rotation intersects at right angles the 
axis of rotation of the shaft. The displacement of the projection of this 
arm along the diameter of the wheel corresponds to the translation of 
the plungers along the bank contacts. Since the displacement of a pro¬ 
jected point along the diameter corresponding to a constant displacement 
along the circumference varies, it is necessary that the arm should rotate 
further near the extremes than when its projection is passing through 
the center. This is accomplished by a fibre wheel having its cir¬ 
cumference divided into segments corresponding to equal displacements 
along the diameter. 

The construction of the line switch bank is indicated in Fig. 13. To 
each switch is assigned a single row of line bank contacts corresponding 
to the 10 first selectors belonging to a particular hundred. Corresponding 
contacts in each bank of the hundred line switches are multipled together 
and terminate in these 10 first selectors. 

The lines are multipled to two spring contacts occurring in each of 
the 10 positions of the bank row. Paralleling these and adjusted so as to 
connect with them readily are the trunk lines of the 10 first selectors. 
Forming the other half of the contacts belonging to each division of the 
bank row are two springs connected with the release and cut off coils, in 
position to engage, respectively, the stationary contacts connected with 
the release trunk and with ground. The contacts of these banks are 
made to come together by means of the plunger arm finger. This finger 
has a small fibre wheel (a) on the end engaging the bank, the other end 
terminating in a fan-shaped metal plate notched at its center, so as to en¬ 
gage the master switch shaft. 

When a call is made, the line switch plunger of the calling line is re¬ 
leased from the shaft and driven into the bank, all the remaining plungers 
being carried to the next position. The switches which have been operat¬ 
ed previously and released remain with plungers directed to the contact 
which they occupied, and should they again be used before the shaft has 
reached the same position returning, they will reoccupy the same trunk. 
The shaft, as it passes from one position to another picks up, as it comes 
to them, all the plungers which have been released from the banks and 
places them again in position to engage an unoccupied trunk. 

Referring to circuit of Fig. 634 an initial impulse over the rotary 
line passes through the springs of the cut-off coil, and the trip magnet, 
energized, attracts its armature (b) and releases the plunger arm at (c), 
allowing the spring (s) to drive it into the bank and close the spring 
contacts of the bank, as here shown. 


THE AUTOMATIC TELEPHONE SYSTEM 


539 


The lines from the telephone are now connected with a first selector 
over one of the 10 trunk lines. A circuit to ground through the cut-off 
relay opens the cut-off springs, leaving the rotary and vertical lines clear 
to the trunks. Any impulse now sent over the lines in no way effects any 
part of the line or master switch. 

Immediately following the operation of the trip magnet, the rotation 
of the shaft is accomplished by the master switch. When the plunger 
closes the bank contacts, main battery through the release magnet is 
thrown upon that contact of the master switch bank which corresponds 
J to the trunk occupied, and upon which is resting the wiper arm of the 
master switch. This bank consists of 10 pairs of insulated contacts. The 
upper row of 10 is multipled with the corresponding release trunks, while 
the lower contacts are all connected to ground through the relay coil of 



Fig. 635. Guide Shaft and Line Unit. 


the master switch. This relay is a double coil of 3,000 ohms resistance, 
constantly energized, but wound so that the direction of the magnetic 
force of one winding is opposed by the other. The wiper arm merely con¬ 
nects the ground contact with the release trunk. 

When the plunger o? the line switch throws battery on this contact, 
through the release magnet, the circuit is closed through one winding of 
the differential relay to ground, while the other winding is shunted out. 
This allows the relay armature to pull down and throw main battery 
upon the circuit leading to the master switch magnet. This magnet, 



540 


TELEPHONOLOGY 


through its armature, causes the pawl to engage the shaft wheel. As this 
armature pulls down, the circuit through the magnet coil is broken at 
springs (S3) and (S4), allowing the armature then to fall back. The 
springs (SI) and (S2), however, have been closed by the movement of the 
fibre wheel, and this retains the conditions at the differential coil un¬ 
changed, even though the wiper arm has passed from its bank contact. 
Consequently the armature of the differential coil remains down. 

When the armature of the master switch magnet falls back therefore, 
the coil again receives battery through the springs operated by it and 
again pulls up and drives forward the shaft wheel. This continues until 
spring (S2) reaches a depression in the fibre wheel and separates from 
(SI). This point then corresponds to a position of the shaft which holds 
the plungers directly over a bank contact and the wiper arm upon a con¬ 
tact free of battery. Since the trip magnet receives its battery through 
the springs of the master switch coil, no switch can trip in while the master 
switch is operating. 



Fig. 637. Floor plan 10,000 line Automatic Exchange. 


The line switch is released from the first selector over the release 
trunk in a manner similar to that in which the first selector is released 
from the connector. The release armature, in pulling up, catches the 
plunger arm (C) and, as it falls back after the impulse, withdraws the 
plunger from the banks. 

A completed connection between two telephones in a ten thousand 
system with diagrammatic circuits of all the switches used in establishing 
the connection is shown in Fig. 636. (See Fronticepiece.) 

The talking circuit is substantially the same as used in nearly all 
manual systems of today. 












































































































































































THE AUTOMATIC TELEPHONE SYSTEM 


541 


It will be noted that with the exception of the connector, each switch 
used in making the connection is cut out of circuit as soon as it has been 
operated, and that the connector relays are the only ones remaining on 
the line when the connection is completed. 



Fio-. 638. Columbus, Ohio, Switchboard Room, 


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542 


TELEPHONOLOGY 


In tracing the operation of a switch from the circuit diagram, it is 
well to remember that the three position side switches all move simulta¬ 
neously, and that in the diagram they are all shown in the third or 
“through” position. 

The exchange battery is maintained at about 46 vqjts, the same set 
of batteries being used for operating the switches and for supplying talk¬ 
ing current to the transmitters. 

The vertical and rotary line relays of the selectors and connectors 
are wound to a resistance of about 300 ohms each, so that the current flow¬ 
ing over the line when operating is about fifteen hundredths of an ampere. 
The operating magnets of the switch, i. e., the vertical, rotary and release 
magnets have about 60 ohms resistance each, and the private magnets 
350 ohms each. The relays are adjusted to operate over a resistance 
varying from 0 to 750 ohms per line. In trunking between widely sepa¬ 
rated exchanges, where the distance is too great lor satisfactory transmis¬ 
sion, the trunks are provided with “repeaters” which relay the impulses 
and also the talking current, the calling subscriber receiving common 
battery for his transmitter from his own exchange instead of from the 
connector in the exchange of a called party. 

To facilitate toll connections, the “O” hole of every calling dial is 
marked “Long Distance”. When the subscriber pulls down the “O”, his 
first selector is stepped up to the 10th or “O” row of contacts. These 
contacts are multipled as usual, but the trunks, instead of terminating 
in second selectors, are wired directly into the toll board, terminating 
in jacks (or keys). The first selector rotating automatically, selects 
the first one of these trunk lines which is not in use. and when the suo- 
scriber pushes his ringing button a signal lamp is lighted in front of the 
operator, who completes the connection in the usual way. 

From the toll board, there are also a number of trunks to line 
switches in the automatic switchboard, and the toll operator is provided 
with a calling dial for calling automatic subcribers. 

In some large exchanges where the toll traffic is very heavy, all the 
subscribers’ lines are brought to jacks in a “switching section”, where 
connections with automatic subscribers may be made direct without the 
use of a callling dial. 

All toll connections are controlled by double supervisory lamp signals 
as in ordinary manual practice. 

Where it is desired to operate an automatic in connection with a 
manual switchboard, an arrangement similar to that used in toll work is 
made, the manual board being designated by a single digit. An auto¬ 
matic subscriber wishing connection to a manual subscriber rotates his dial 
from hole No. 1, for instance, (which may be marked “Main”) and 
pushes his ringing button, thereby lighting a lamp signal in front of 
the operator in the manual trunking section. 

Any first selector level, or row of contacts, not in use may be wired 
to a special board or desk; so that by a single movement o. the dial any' 
subscriber may signal an operator or clerk. 

This feature is made use of for calling Fire Alarm, Police Alarm, 
Trouble and Information, Rural lines, or for any purpose where especially 
quick service is desired. 

Private branch exchanges are arranged to be operated entirely auto¬ 
matic or semi-automatic, as desired, the flexibility of the system permit¬ 
ting of almost any desired combination. 



Fig. 639. Grand Rapids, Mich., Switchboard Room, Line Swith Addition. 


54 3 




































544 


TELEPHONOLOGY 


A private branch exchange having several trunks, will have one num¬ 
ber for all, the connectors in this particular hundred group being arranged 
to rotate automatically, selecting the first one of the trunks not in use. 

The four-party selective ringing system is arranged for in a simple 
manner by having the party line contacts in the connector banks multi- 
pled through four different groups of connectors, the groups being sup¬ 
plied with ringing current of different frequencies. The four subcribers, 
although on the same line, have different hundred numbers, as for in¬ 
stance, 7256, 7356, 7456, 7556, and the ringers being of the harmonic 
type respond only to ringing current of the proper frequency. 



Fig. 640. General view Switchboard Room, Omahha, Neb. 



























THE AUTOMATIC TELEPHONE SYSTEM 


545 


Perhaps the most important development in automatic telephony in 
recent years is the installation and operation of the district station or 
as it is sometimes called the sub-station. The district station consists 
simply of one (or more) 100 line units, such as have been described, its 
location being changed from the central office to the center of distribution 
of a suburb or any section of the city. The subscribers’ lines are brought 
to this station and from the district station to the main exchange incoming 
and outgoing trunks are provided sufficient to take care of the maximum 
traffic. 


Fig. 641. A 500-line section of exchange, Omaha, Neb. 

The 100 unit being only 20 X 33 inches by 5 ft. high, may be placed 
in small quarters. It is usually located in a small room of an office or 




























































546 


TELEPHONOLOGY 


store building, or in a small frame or cement building constructed for it. 
A comprehensive system of signals indicate in the Main exchange any 
trouble which may occur in the district station and every subscriber’s 
line, as well as every trunk line may be tested direct from the Wire Chief’s 
desk in the main exchange. The line switch being comparatively simple 
in construction, requires little attention and an occasional inspection suf¬ 
fices to keep the switchboard in good working order. 

A number of these district stations have been in operation for a con¬ 
siderable time with entirely satisfactory results. 

The tremendous saving in construction, etc., which is effected by 
their use is apparent when it is considered that 15 to 20 trunks are ordi¬ 
narily sufficient to serve 100 district station subscribers. 


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